Push-button telephone

The concept of push-buttons in telephony originated around 1887 with a device called the micro-telephone push-button, but it was not an automatic dialing system as understood later. This use even predated the invention of the rotary dial by Almon Brown Strowger in 1891.[3] The Bell System in the United States relied on manual switched service until 1919, when it reversed its decisions and embraced dialed, automatic switching. The 1951 introduction of direct distance dialing required automatic transmission of dialed numbers between distant exchanges, leading to use of inband multi-frequency signaling within the Long Lines network while individual local subscribers continued to dial using standard pulses.

As direct distance dialing expanded to a growing number of communities, local numbers (often four, five or six digits) were extended to standardized seven-digit named exchanges. A toll call to another area code was eleven digits, including the leading 1. In the 1950s, AT&T conducted extensive studies of product engineering and efficiency and concluded that push-button dialing was preferable to rotary dialing.[4]

After initial customer trials in Connecticut and Illinois, approximately one fourth of the central office in Findlay, Ohio, was equipped in 1960 with touch-tone digit registers for the first commercial deployment of push-button dialing, starting on 1 November 1960.[5][6]

In 1962, Touch-Tone telephones, including other Bell innovations such as portable pagers, were on display for the public to try out at the Bell Systems pavilion at the Seattle World's Fair. Ref. YouTube video entitled "Vintage Roadtrips – 1962 Seattle World's Fair".

On 22 April 1963 President John F. Kennedy started the countdown for the opening of the 1964 World's Fair by keying "1964" on a touch-tone telephone in the Oval Office, starting "a contraption which will count off the seconds until the opening".[7] On November 18, 1963, the first electronic push-button system with touch-tone dialing was commercially offered by Bell Telephone to customers in the Pittsburgh area towns of Carnegie and Greensburg, Pennsylvania,[4][8] after the DTMF system had been tested for several years in multiple locations, including Greensburg. This phone, the Western Electric 1500, had only ten buttons. In 1968 it was replaced by the twelve-button model 2500, adding the asterisk or star (*) and pound or hash (#) keys.[9] The use of tones instead of dial pulses relied heavily on technology already developed for the long line network, although the 1963 touch-tone deployment adopted a different frequency set for its dual-tone multi-frequency signaling.

Although push-button touch-tone telephones made their debut to the general public in 1963, the rotary dial telephone still was common for many years. Sales of touch-tone telephones picked up speed during the 1970s,[10] though the majority of telephone subscribers still had rotary phones, which in the Bell System of that era were leased from telephone companies instead of being owned outright.[11] Adoption of the push-button phone was steady, but it took a long time for them to appear in some areas.[12] At first it was primarily businesses that adopted push-button phones.[13]

The touch-tone system required the need for additional equipment at the telephone exchange to decode the tones. However, most telephone exchanges in the early 1970s only supported pulse dialling based on the Strowger switch system, restricting touch-tone telephones to some private branch exchanges (PBX). Tone to pulse converters were later added to linefinder groups in Step by Step offices to allow some subscribers to use DTMF sets. British companies Pye TMC, Marconi-Elliott and GEC developed a new digital push-button telephone technology, based on metal-oxide-semiconductor (MOS) integrated circuit (IC) chip technology. It was variously called the "MOS telephone", the "push-button telephone chip", and the "telephone on a chip". It used MOS integrated circuit (MOS IC) logic, with thousands of MOS transistors on a chip, to convert the keypad input into a pulse signal. This made it possible for push-button telephones to be used with pulse dialling at most telephone exchanges.[14][15]

MOS telephone technology introduced a new feature to push-button telephones: the use of MOS memory chips to store phone numbers, which could then be used for speed dialing at the push of a button.[14][15][16] This was demonstrated in the United Kingdom by Pye TMC, Marcno-Elliot and GEC in 1970.[14][15] Between 1971 and 1973, Bell Laboratories in the United States combined MOS technology with touch-tone technology to develop a push-button MOS touch-tone phone called the "Touch-O-Matic" telephone, which could store up to 32 phone numbers in an electronic telephone directory stored on memory chips. This was made possible by the low cost, low power requirements, small size and high reliability of MOS transistors, over 15,000 of which were contained on ten IC chips, including one chip for logic functions (such as shift registers and counters), one for the keypad dial interface, and eight for memory storage.[17] By 1979, touch-tone phones were gaining popularity,[13] but it was not until the 1980s that the majority of customers owned push-button telephones in their homes; by the 1990s, it was the overwhelming majority.

Some exchanges no longer support pulse-dialing[12] or charge their few remaining pulse-dial users the higher tone-dial monthly rate[18] as rotary telephones become increasingly rare.[19][20][21] Dial telephones are not compatible with some modern telephone features, including interactive voice response systems, though enthusiasts may adapt pulse-dialing telephones using a pulse-to-tone converter. Most, but not all VoIP analogue Telephone Adapters (ATA) will only support DTMF dialling.

DTMF keypad layout

The standard layout of the keys on the touch-tone telephone was the result of research of the human-engineering department at Bell Laboratories in the 1950s under the leadership of South African-born psychologist John Elias Karlin (1918–2013), who was previously a leading proponent in the introduction of all-number-dialing in the Bell System. This research resulted in the design of the DTMF keypad that arranged the push-buttons into 12 positions in a 3-by-4 position rectangular array, and placed the 1, 2, and 3 keys in the top row for most accurate dialing.[27] The remaining digits occupied the lower rows in sequence from left to right; the 0, however, was placed into the center of the fourth row, while omitting the lower left and lower right positions.

The DTMF keyboard layout broke with the tradition established in cash registers (and later adopted in calculators and computers) of having the lower numbers at the bottom.[28] This was due to research conducted by Bell Labs using test subjects unfamiliar with keypads. Comparing various layouts including two-row, two-column, and circular configurations, the study concluded that while there was little difference in speed or accuracy between any of the layouts, the now familiar arrangement with 1 at the top was the most favourably rated.[29]

The engineers had envisioned telephones being used to access computers, and surveyed business customers for possible uses. This led to the addition of the number sign (#, pound or diamond in this context, hash, square or gate in the UK, and octothorpe by the original engineers) and asterisk or star (*) keys in 1969. Later, the hash and asterisk keys were used in vertical service codes, such as *67 to suppress caller ID in the Bell System.

In military telephone systems four additional signals (A, B, C, D) were defined for signaling call priority.