This article was initially written as part of the IEEE STARS program.
The telephone is the equipment that a person uses to access the telephone network and talk to another user. Along with telephone transmission and switching, the telephone is one of three major subsystems that make up a telephone network. At its simplest, a telephone translates complex sound waves into their electrical analogs for transmission, and conversely converts those electrical waves back into audible and intelligible speech. Over the century following the first working telephones, the instruments evolved in ways that improved their efficiency, reliability, ergonomics, and convenience. This article covers neither cellular telephones nor other special purpose telephones.
Along with telephone transmission and switching, the telephone instrument—the user interface—is one of the three major subsystems that make up a telephone network. To a substantial extent, the history of innovations in telephony is an American story, in part because as late as the 1950s the U.S. had more than half of the world’s telephones, and in part because AT&T, operator of the Bell System and its research arm, Bell Telephone Laboratories, played a dominant role in telephone innovation. Over the century following the beginning of telephone service, the instruments evolved in ways that improved their quality, efficiency, reliability, and ergonomics, keeping in step with advances in transmission and switching.
By the mid-1850s, the telegraph had been established as the major electrical communications system throughout much of the industrialized world. It was not a large intellectual leap from using an electric current to transmit the on-off electrical pulses of telegraphic code to using that electric current to send sounds and human speech. Charles Bourseul in France published a description of how speech might be transmitted electrically in 1854. Phillip Reis in Germany constructed and demonstrated an apparatus designed to do just that in 1861, though there is little consensus on how well it worked. Reis coined both the German word “fernsprecher” and the English word “telephone” for his device, but it never became more than a curiosity that faded from view with Reis’s early death. Others continued to make the same intellectual leap, most notably Elisha Gray, an established American telegraph inventor, and Alexander Graham Bell, a young man trying to make his mark. The two men’s work largely paralleled each other for several years beginning in 1873; they both began by trying to develop a harmonic telegraph, a device that would transmit multiple telegraph messages over a single wire by sending each one on a separate electrical frequency, by 1874, they were applying what they had learned to solving the problem of the transmission of speech. In that year, Alexander Graham Bell came up with a key concept, which he called “undulating current.” That is, to transmit speech one wanted a continuously varying current in the form of a wave analogous to the original sound wave—not the intermittent current of telegraphy. Bell sought to construct a device to translate sound waves into electrical waves. His device, later known as the “gallows telephone” due to its shape, produced an undulating current by electromagnetic induction. With it, Bell transmitted speech sounds on 2 June 1875, but not intelligible speech.
On the basis of this work, on 14 February 1876, Bell filed a patent application with the U.S. Patent Office entitled “Improvement in Telegraphy.” While many of the claims related to the application of an undulating current to the harmonic telegraph, the most historically significant claim was for its application to the transmission of speech. On the same day, Gray filed a patent caveat, a document stating that he was working on inventing a telephone and anticipated filing a patent application at a future date. The question of who deserves credit for the invention of the telephone was examined in detail by the courts, and later by historians. Gray undoubtedly hurt his case by not pursuing his claim; he never filed for a patent. Bell on the other hand energetically promoted his devices. (See the article by B. Finn cited below for details.) In Bell’s key patent, 174,465, awarded on March 7, 1876, he received credit for his induction transmitter and receiver together with the all-important principle of transmission by undulating current. In other countries this last claim was not allowed, thus making it possible for others to compete with different instruments.
While the Patent Office was evaluating his application, Bell turned his attention from electromagnetic induction to variable resistance. Using variable resistance, he transmitted the first telephone message on 10 March 1876 in a Boston, Massachusetts, attic. Bell and his assistant Thomas Watson wrote different versions of the famous first sentence in their respective notebooks. Bell wrote what he said, “Mr. Watson come here I want to see you” while Watson wrote what he heard, “Mr. Watson come here, I want you.” The device became known as the “liquid transmitter” since the continuously varying current was created by the dipping of a needle (which was attached to a diaphragm) in a small container of acidulated water. This liquid transmitter was part of an electric circuit, which also contained a battery to provide the current, and a tuned-reed receiver, on which Watson, down the attic’s hall, heard Bell’s voice.
Within a month, Bell had abandoned variable resistance transmitters for further and ultimately more fruitful development of electromagnetic devices. On 30 January 1877, Bell received a second patent, No. 186,787, for a working electromagnetic telephone.
Bell began demonstrating his invention and with several associates formed the Bell Telephone Company to exploit it. Bell ceased active participation in the company in 1878, leaving further development to others. These early telephones used the same electromagnetic instrument for both transmitter and receiver. However, its use as a transmitter was less than satisfactory because the electromagnetic instruments use only the energy in the sound waves as the source of the electric current, severely limiting the amount of current available. Variable resistance transmitters, on the other hand, use the sound waves to modulate an existing and potentially larger current already present in the circuit, typically via a battery, and thereby could amplify the voice signal. Indeed, until vacuum tubes became available in the mid-1910s, variable resistance transmitters were the only way to amplify the signal. With variable resistance transmitters providing increased current, electromagnetic receivers performed satisfactorily in converted the electric signal back into sound waves.
The commercial phones introduced by the Bell Telephone Company in 1878, for use in the earliest telephone exchange, contained two electromagnetic devices: each shaped to be held in the hand, one for use as a transmitter and the other as a receiver. They became known as “butter stamps” owing to their distinctive shape. The phones sported two other important components, both invented and patented by Bell’s former assistant, Thomas Watson, the fledgling company’s engineer. These comprised a hand-cranked magneto that the subscriber used to generate a current to signal the switchboard operator to make a call, and a two-bell polarized ringer that the operator could use to signal to the subscriber when there was an inbound call. Hilborne Roosevelt invented the switch hook in 1877, whereby the telephone calling circuit could be opened and closed by picking up and hanging up the receiver, rather than by using a separate switch.
Variable Resistance Transmitters
Within two years of Bell’s invention, several inventors had developed workable variable resistance transmitters, all using the principle that the resistance between two conductors in loose contact varied with the pressures applied to them. Working in the United States, Thomas Edison in 1877 devised a transmitter using a button made of a pressed cake of carbon lampblack and a stiff metal diaphragm. He added an induction coil, which matched the currents and impedances of different parts of the circuit. Edison’s transmitter came into use in several countries, including Great Britain, and in U.S. telephone exchanges operated by Western Union Telegraph, though these Edison transmitters were gradually retired after Western Union sold its telephone business to Bell in 1879.
Around the same time, Emile Berliner, also working in the United States, devised a variable resistance transmitter that utilized a solid steel ball pressed against an iron diaphragm. After the Bell Company acquired Berliner’s patent rights, the company’s Francis Blake built upon Berliner’s work, devising another carbon-button based transmitter. The Blake transmitter worked well over the short distances typical of early telephone exchanges, and became standard in Bell telephones in the 1880s. It was also widely adopted in Britain and other countries.
Meanwhile in England, David Hughes devised a variable transmitter using carbon pencils in loose contact with each other, providing several points of contact and thus potentially better amplification. Henry Hunnings, also in England, developed the first transmitter using powdered carbon. This initially produced superior amplification, but over time the powdered carbon shifted and compressed, reducing amplification below satisfactory levels.
There was an additional round of innovation in the following decade. Edison returned to telephone work, and in 1886 devised an improved granular carbon transmitter using roasted powdered anthracite coal granules, which did not readily pack together, and an improved chamber to hold the button. Edison sold this invention to Bell. Finally, Bell’s Andrew White improved on Edison’s invention in 1890 with the solid back transmitter, which eliminated the packing problem for a transmitter used in a fixed position. It became the standard for transmitter design in the United States and through much of the world for the next 35 years.
By the end of the 1870s, all of the basic components for a working telephone had been developed: variable resistance transmitter, electromagnetic receiver, magneto, ringer, switch hook, and induction coils. So, while in the late 1870s one Bell System model rapidly replaced another, in 1882 the Western Electric Company, which had recently become the manufacturing arm of the Bell Company, introduced a standard model which remained in production, with incremental improvements, through most of the decade. It was a large wooden wall set with three separate boxes attached to a backboard. The top box contained the ringer, the magneto, and, at its left side on a switch hook, the electromagnetic receiver. The middle box contained a Blake variable-resistance transmitter and an induction coil, and the bottom box two wet-cell batteries. Since Blake transmitters produced only enough current to be usable over short distances, typically under 20 miles, early long-distance networks required the use of Hunnings transmitters, mounted horizontally to minimize packing, on special long-distance phones. In the 1890s, both Blake and Hunnings transmitters gave way to White’s solid block transmitters, and the central box on the standard wall set gave way to a transmitter affixed to a metal arm.
European telephone designs in this period were similar to American ones for a variety of reasons, including the presence of Western Electric in all European markets--except, after the early 1890s, Germany. But there were some differences—most notably the appearance of telephones with combined handsets, containing a both a transmitter and a receiver in a single piece. These sets were more convenient to hold and use, but they suffered from the following drawbacks:
1) The positional effect, where the transmitter decreases in efficiency as the carbon falls away from the two electrodes as the transmitter moves farther from the vertical;
2) Sidetone, where feedback from sound going directly from the transmitter to the receiver, both through the air and through the electrical connection between the transmitter and the receiver, induces the speaker to compensate by speaking more softly; and
3) Howl, or the feedback between the transmitter and receiver from vibrations traveling in the handset.
One notable combined handset telephone, introduced by Ericsson of Sweden in multiple European markets, turned the magneto into a decorative external frame that also held the handset cradle and switch hook. While convenient for the subscriber to hold, and pleasing to look at, it did not solve the problems inherent in combined handsets.
Common Battery Sets
Since telephones are just one element in a network, a change elsewhere in the network could lead to a change in telephone design. One example was the common battery system, introduced in the mid-1890s in United States and soon after in Britain. There a low dc current was sent from the telephone exchange down the transmission wire to all subscribers. Once installed in a given local exchange, this system removed the need for both the magneto and the local batteries on the telephone, allowing for a new, smaller, and more simplified design for the subscriber’s set. Common battery sets also required far less maintenance since there were no local batteries that needed periodic replacement. This arrangement reduced costs and improved reliability.
Since common battery systems were installed one exchange at a time, and were for many years not suitable for longer circuits, such as those typically found in rural areas, magneto phones continued to be widely used. Common battery circuits also required up-to-date higher efficiency transmitters, like the White solid back. Therefore, when the British Post Office acquired the privately operated National Telephone Company in 1912, it had to retire all of the Ericsson hand-set magneto telephones before it could update the exchanges.
Common battery systems also made possible the development and large-scale introduction of desk sets, telephones designed to sit on a desk or table, which for many telephone subscribers was a more convenient arrangement. Western Electric introduced a series of desk stands between 1897 and 1904, leading to the Model 20, commonly known as the “candlestick” after its shape. With minor modifications it remained the most widely used model for over 25 years. To make a phone small enough for a desk top, the ringer and the induction coil, collectively known as the network, were placed in a separate box on the wall. This box was known as the subscriber set or subset, and later included additional components designed to decrease sidetone and electrical interference. Thus, the desk stand contained just the receiver, transmitter, and switch hook. Similar phones soon became popular in Europe.
Dial telephones were tied to the invention of automatic switching by Almon Strowger and its development by Automatic Electric, the Chicago-based company formed to exploit Strowger’s patent. Automatic switching required that the subscriber send signals to operate the switch from his or her telephone, since a human operator would no longer routinely handle the call. Alexander Keith and two co-workers devised a practical device—the numbered telephone dial—in 1896, and Automatic Electric began selling systems of Strowger switches and dial telephones to some of the new, independent, non-Bell telephone companies. These appeared in the United States after the expiration of Bell’s second patent in 1894.
The rotations of the dial sent electrical pulses to the switch to indicate the digits of the telephone number. Dialing a 1 produced one pulse as the dial returned to its original position; dialing a 9 produced nine pulses; and so on. Automatic Electric produced both desk and wall dial telephones. By 1914, over 400,000 dial telephones were in service in independent telephone company exchanges in the United States. In 1919, the Bell System installed its first dial telephones in Norfolk, Virginia, and then undertook the enormous multi-decade task of converting its exchanges from manual telephones and switches to dial telephones and automatic switches, one exchange at a time.
The British Post Office installed the first dial telephones in Great Britain, in Epsom, Surrey, in 1912; most other countries moved to dial telephones gradually after World War One.
The Structure of the Telephone Industry and the Design of Telephones
The nature of the telephone industry played a major role in shaping the design of telephones in ways atypical of most consumer durables. In virtually every country, except the United States and several provinces in Canada, the post office managed telephone service as a government monopoly. For example, telephone system nationalization occurred in France in 1889, Britain in 1912, and Sweden in 1918. In the United States, while the telephone industry remained in the private hands of AT&T, it operated after 1913 as a government sanctioned, regulated, private monopoly. It controlled all long distance lines and over 80 percent of local lines with the remaining independent companies local lines connected to AT&T’s long lines, and generally following AT&T’s business model. In all these monopolies, public or private, telephones were leased to subscribers as part of their monthly service, and not owned by subscribers. Thus, to a large extent telephones were not subject to consumer fashion. For the most part they were designed for efficiency and durability, rather than style, and remained unchanged for many years. A subscriber had at most a limited choice of a few styles and little opportunity to change to a newer model. Over time, Western Electric and other manufacturers made incremental improvements in a variety of components, including transmitters and receivers, to improve the technical quality of the service.
The Revival of Combined Handsets
The introduction of combined handset telephones in the United States is a partial exception to the rule that telephone designs were not subject to consumer fashion, and therefore remained unchanged for years. There was subscriber convenience and style in having the transmitter and receiver in a single handset; and in certain countries, including France, combined handset telephones were always a popular choice. In other countries, including the United States, and after the early 20th century, Great Britain, they were not available, because while stylish and convenient they were technically inferior, as noted above. But by 1918, Bell officials realized that some affluent subscribers were replacing their Bell-provided desk sets with these more stylish combined handset phones, which were imported from Europe or made by independent American firms. Concerned about the integrity of its network, Bell began a research program that year to design a combined handset that would match the performance of the desk stand telephone.
By 1926, the work at Bell Labs had advanced to the point where there was a new carbon transmitter with greatly reduced positional effects, and a combined handset with minimal howling. AT&T placed this new handset, the E1, on a shortened candlestick base, and began offering it to subscribers for an additional monthly fee, even though Bell Labs President Frank Jewett advised against the plan, calling for customer field trials first. Jewett proved prescient as a large percentage of the transmitters in these phones failed within two years. The Labs redesigned the transmitter, added an anti-sidetone circuit, and introduced two successive bases, the circular 102 and then the oval 202, designed specifically for the handset. By 1931, 26 percent of Bell subscribers had the newer phones. Still, the transmitters aged poorly, typically requiring repair or replacement within four years. The newer phones, like the candlestick before it, came in black, but Western Electric painted small quantities of them a handful of other colors. Telephone companies did not publicize these colored phones, though they were available to subscribers for an extra monthly charge.
Bell Labs researchers went back to work, and the result in 1937 was a completely new telephone design, the Western Electric model 302. It featured a completely redesigned transmitter and a new handset designated the F1. More significantly it was a complete desk telephone; all of the familiar components of the subscriber set were redesigned and made smaller so that everything could be housed in the telephone itself. The 302 was efficient, durable, and popular, and remained in production through the early 1950s. By 1941, 80 percent of Bell telephones in service featured combined handsets. The 302 was also the first handset where Bell explicitly considered aesthetics. After an external design competition in 1934 failed to produce a telephone that met the Labs’ technical requirements, Bell hired industrial designer Henry Dreyfuss who, in conjunction with the company’s engineers, designed the 302. Dreyfuss and his firm would design all of AT&T’s phones through the 1960s. The first 302s had a black metal case, but beginning in 1941, 302s came with cases of black Bakelite plastic. Bell placed over 25 million 302 series phones in service between 1937 and 1951.
The British Post Office reintroduced a combined handset phone in 1929. L. M. Ericsson of Sweden introduced a combined handset phone with a plastic Bakelite case in several European countries in 1931, and an improved model, similar to the Western Electric 302 in 1938. The British Post Office offered the latter phone as its model 300, though it was popularly known as the “Neophone.”
Developments after World War II
In 1951, the Bell System introduced a new standard telephone, the Western Electric 500, developed again at Bell Labs. The 500 featured evolutionary improvements over the 302, which it gradually replaced in the first half of the 1950s. These improvements reduced costs for AT&T while providing an improved experience for the subscriber. There were several notable improvements. The handset (type G1) was 25 percent lighter, with a flat back that was easier to hold. The redesigned transmitter and receiver were five decibels more efficient (and thus put a stronger signal on the subscriber’s wire), enabling their use on longer local exchange circuits without modification. The numbers, which had been under the finger hole in earlier dials, were now outside the dial, for better readability and reduced wear. For the first time, the ringer volume could be adjusted by the subscriber. Bell Labs also designed the 500 for easier, less expensive repair in the field. The case, again designed by Henry Dreyfuss, had a more streamlined, rounded design, and was made from a new thermoplastic material with reduced production costs. While Bell initially marketed the 500 in black only, the new plastic could be manufactured in almost any color, leading to the 1954 introduction and advertisement of telephones in a range of colors, available for an extra monthly charge. A wall set, popular especially in kitchens, followed in 1956. The 500 had an unusually long production run until 1986. Similar phones followed in other countries, including the model 706, made by Ericsson for the British Post Office in 1959, and the Ericsson Dialog, introduced in multiple European countries in 1962.
Ericsson started another trend with the first one-piece phone, the Ericofon. The Ericofon had its dial in its base, and the phone was hung up simply by putting it down. Ericsson introduced this phone in 1954 through the Swedish telephone authority, for institutional use in hospitals and similar facilities. Because of consumer interest, telephone authorities began offering the Ericofon for general use, first in Sweden in 1956, and Denmark in 1957, and eventually throughout the world. It typically rented for an extra charge. The Australian Postmaster-General’s Department, for example, began renting the Ericofon in 1963. It was the first phone design since the early 20th century that was marketed and adopted primarily for style rather than function.
AT&T introduced a very different phone to be marketed for its style in 1959. The Princess phone featured a wide, low, oval shape, and was marketed with the slogan, “it’s little, it’s lovely, it lights.”
The initial design had several flaws. The ringer, too large to fit in the telephone, was in a separate box at the wall, leaving the set too light in weight and likely to follow a lifted handset cord and fall off the table. After a redesign fixed these problems in 1963, the phone became a popular second household set.
Finally, in 1965, AT&T introduced the first dial-in-handset phone, the Trimline. The Trimline required a major engineering effort to reduce the size of several components–the ringer, the receiver, and most notably the dial, which was reduced in size by removing the empty space between the 1 and the 0, and making the finger stop movable. It was the last major design introduced by the Bell System before the system’s breakup in 1984. Like the Princess, it rented for an additional monthly charge. One additional change during this period, the introduction of touch-tone service, led to alternate versions of Bell’s telephones featuring keypads rather than dials.
Touch-tone service transmitted tones at a unique pair of frequencies for each key to indicate the digits of the number that the subscriber wished to reach. These tones, working in conjunction with new equipment added to existing switches, were able to travel through the entire network rather than just as far as the local switch, and thus had the potential for a variety of additional uses. Bell introduced touch-tone service gradually through the Bell System, beginning with two exchanges in 1963. By 1976, Bell had equipped 70 percent of its exchanges for touch-tone service. Bell’s additional monthly charges for this option slowed its rate of adoption. Early touch-tone phones had ten keys, corresponding to the finger holes on the rotary dial. In 1968, Bell added the * and # keys to enable these phones to access a range of advanced features, producing the standard 12-button key pad. Touch-tone technology spread slowly to other countries. For example, touch-tone service became available in Sweden in 1978, using telephones supplied by Ericsson.
Through the 1960s, all telephone transmitters continued to be derivatives of the carbon variable-resistance transmitters developed in the 19th century. But in 1962, Gerhard Sessler and Jim West at Bell Laboratories developed an entirely new type of transmitter, the foil electret. Beginning in the late 1970s, foil electrets began to replace carbon transmitters in telephones. Foil electrets provided multiple advantages: small size, low cost, broad frequency response, and solid-state durability.
The long history of there being only a limited number of telephone models, with those models being determined by and rented from the local telephone monopoly, began to change in 1975, after the United States Supreme Court ruled that subscribers could own their own telephones. This led to a proliferation of telephone manufacturers and designs, and a shift from telephones designed to work without fail for many years to telephones as a disposable consumer good. Competition in telephone sets led to much innovation, leading to, among other things, the widespread adoption of cordless phones. Sweden allowed private telephone ownership in 1980 and Great Britain as well in 1981, the latter as part of the privatization of its postal telephone system. Other countries made the transition as well, typically when they too privatized their government-owned telephone systems. With this change in the nature of service, an era in telephony came to a close.
The author wishes to acknowledge the many useful suggestions made by Alexander Magoun, Managing Editor of the STARS program, several members of the STARS editorial board, and William Caughlin, Corporate Archivist, AT&T.
- 1861, Phillip Reis demonstrates and names a telephone, which transmits sound
- 1875, Alexander Graham Bell succeeds in transmitting speech sounds
- 1876, Bell succeeds in transmitting intelligible speech
- 1877, Edison, Berliner, Hughes, and Hunnings invent solid variable-resistance transmitters
- 1878, Francis Blake invents a variable resistance, solid carbon transmitter that Bell adopts
- 1878, Thomas Watson receives patents for the magneto and the ringer
- 1886, Thomas Edison invents the granular carbon transmitter
- 1890, Anthony White develops the solid-back transmitter
- 1892, L. M. Ericsson of Sweden introduces the first widely used handset telephone
- 1896, Alexander Keith, John Erickson, and Charles Erickson invent the dial telephone
- 1896, First common battery telephones go into service, in Worcester, Massachusetts
- 1927, First combined handset telephone installed in the Bell System
- 1937, Western Electric introduces the Model 302 desk telephone with an improved handset
- 1949, Western Electric Model 500 introduced; kept in production until 1986
- 1956, Ericsson Ericofon: the first one-piece, modern phone marketed on the basis of style
- 1962, Gerhard Sessler and James West of Bell Labs invent the foil electret microphone
- 1963, Touch Tone dialing introduced by AT&T
- 1977, Consumers in the U.S. could own rather than lease phones; other countries follow
References of Historical Significance
Alexander Graham Bell. 1877. “Improvement in Electrical Telegraphy”. U. S. Patent No. 186,787, 30 January 1877, filed 15 January 1877
Alexander E. Keith, John Erickson, and Charles J. Erickson. 1896. “Calling Device for Telephone Exchange”. U.S. Patent No. 597,062, 11 January 1898, filed 20 August 1896
W. C. Jones and A. H. Ingles. “The Development of a Handset for Telephone Stations”. Bell System Technical Journal 11, no. 2 (April 1932), p. 245-63
R. L. Deininger. 1960. “Human Factors Engineering Studies of the Design and Use of Pushbutton Telephone Sets”. Bell System Technical Journal 29, no. 4 (July 1960), p. 995-1012
Gerhard M. Sessler and James E. West. 1962. “Electroacoustic Transducer”. U.S. Patent No. 3,118,022, 14 January 1964, filed 22 March 1962
References for Further Reading
Sally Clarke. 1998. “Negotiating between the Firm and the Consumer: Bell Labs and the Development of the Modern Telephone,” in Karen R. Merrill, ed. The Modern Worlds of Business and Industry, p. 161-82. Turnhout, Belgium: Brepols
Andrew Emerson. 1986. Old Telephones. Princes Risborough, England: Shire Publications
L. M. Ericsson Corporation. n.d.. The History of Ericsson (www.ericssonhistory.com). Accessed 14 March 2013
M. D. Fagan, ed.. 1975. A History of Engineering and Science in the Bell System: The Early Years 1875-1925, p. 59-194. Murray Hill, NJ: Bell Telephone Laboratories
Bernard Finn. 2009. “Bell and Gray: Just a Coincidence?”. Technology and Culture, Vol. 50, no. 1 (January 2009), p. 193-201
Ralph O. Meyer. 2005. Old-Time Telephones! Designs, History, and Restoration, 2nd edition. Atglen, PA: Schiffer Publishing
P. J. Povey and R. A. J. Earl. 1998. Vintage Telephones of the World. London: Peter Peregrinus
About the Author
Sheldon Hochheiser is archivist and institutional historian at the IEEE History Center in Hoboken, New Jersey. Prior to joining IEEE, he spent sixteen years as corporate historian for AT&T, acting as both subject matter expert on AT&T history and manager of the corporate archives. While at AT&T, Dr. Hochheiser curated historical exhibits, completed oral histories with company executives, and studied every aspect of the history of the telephone in the United States. He earned a Ph.D. in the History of Science at the University of Wisconsin, and a B.A. in Chemistry-History at Reed College.
- 1 Citation
- 2 Introduction
- 3 Invention
- 4 Other Components
- 5 Variable Resistance Transmitters
- 6 Telephone Sets
- 7 Common Battery Sets
- 8 Dial Telephones
- 9 The Structure of the Telephone Industry and the Design of Telephones
- 10 The Revival of Combined Handsets
- 11 Developments after World War II
- 12 Acknowledgements
- 13 Timeline
- 14 Bibliography
- 15 About the Author