Atelephone keypad is akeypad installed on apush-button telephone or similartelecommunication device for dialing atelephone number. It was standardized when thedual-tone multi-frequency signaling (DTMF) system was developed in theBell System in the United States in the 1960s – this replacedrotary dialing, that had been developed for electromechanical telephone switching systems.[1] Because of the abundance of rotary dial equipment still on use well into the 1990s, many telephone keypads were also designed to be backwards-compatible: as well as producing DTMF pulses, they could optionally be switched to produce loop-disconnect pulses electronically.
The development of the modern telephone keypad is attributed to research in the 1950s by Richard Deininger under the directorship ofJohn Karlin at the Human Factors Engineering Department ofBell Labs.[2][3] The modern keypad is laid out in a rectangular array of twelve push buttons arranged as four rows of three keys each. For military applications, a fourth column of keys was added to the right for priority signaling in theAutovon system in the 1960s. Initially, between 1963 and 1968, the keypads for civilian subscriber service omitted the lower left and lower right keys. These two keys are commonly labelledstar,⚹, andnumber sign/hash,#, respectively, and produce the signals associated with those symbols. These keys were added to provide signals for anticipated data entry purposes in business applications, but found use inCustom Calling Services (CLASS) features installed inelectronic switching systems.[4]
The layout of the digit keys is different from that commonly appearing oncalculators andnumeric keypads. This layout was chosen after extensivehuman factors testing at Bell Labs.[3][5] At the time (late 1950s), mechanical calculators were not widespread, and few people had experience with them.[6] Indeed, calculators were only just starting to settle on a common layout; a 1955 paper states "Of the several calculating devices we have been able to look at ... Two other calculators have keysets resembling [the layout that would become the most common layout] ... . Most other calculators have their keys reading upward in vertical rows of ten."[5] Meanwhile, a 1960 paper – just five years later – refers to today's common calculator layout as "the arrangement frequently found in ten-key adding machines".[3] In any case, Bell Labs' testing found that the telephone layout with 1, 2, and 3 on the top row, was slightly faster in use than the calculator layout with them in the bottom row.
In addition to the numbers, theITU recommends two additional keys: the "star key", labeled⚹, and the "square key", labeled⌗.[7] The square key is often known as thepound key,hash key oroctothorp.
The precise symbols to be used for the star and square keys is not standardised:asterisk operator (∗) andsextile (⚹) have been recommended for the star key,[8][9] and a simple asterisk* is often used. The "square key" is almost invariably replaced with the# (number sign). A 1973 US patent (3,920,926) by the Northern Electric Company calls them "sextile or asterisk" and "octothorp".[10]
These can be used forspecial functions. For example, in the UK, users can order a 7:30 am alarm call from aBTtelephone exchange by dialing:⚹55⚹0730#.[11]
The Greek symbolsalpha andomega had been suggested originally for these keys. John A. Koten (1929–2014), a corporate communications specialist withBell Labs in Chicago, claimed credit for the choice of star and number sign, reasoning that the new keys would be easier to explain to a public already familiar with typewriter symbols.[12]
In the Americas and a number of other countries, most dials and, later, keypads also bear letters according to the following system:
| Key | Letters |
|---|---|
| 1 | none (on some older telephones, QZ) |
| 2 | ABC |
| 3 | DEF |
| 4 | GHI |
| 5 | JKL |
| 6 | MNO (on some older telephones, MN) |
| 7 | PQRS (on older telephones, PRS) |
| 8 | TUV |
| 9 | WXYZ (on older telephones, WXY) |
| 0 | none (on some telephones, "OPERATOR" or "OPER") |
In the UK, dials and keypads also bore letters, though these were later dropped. They were arranged as follows:
| Key | Letters |
|---|---|
| 1 | none |
| 2 | ABC |
| 3 | DEF |
| 4 | GHI |
| 5 | JKL |
| 6 | MN |
| 7 | PRS |
| 8 | TUV |
| 9 | WXY |
| 0 | OQ |
Assigning the letter O to the zero makes sense, as in British speech, "oh" is often said rather than "nought" or "zero"; Q is visually similar to O, causing plausible confusion. Therefore, two possible mistakes were avoided.
These letter assignments have been used for multiple purposes. Originally, they referred to the dialable letters oftelephone exchange names. In the mid-20th century United States, before the switch toAll-Number Calling, telephone numbers had seven symbols, including a two-symbol prefix which was expressed in letters rather than digits, e.g.;KL5-5445. TheUK telephone numbering system used a similar two-letter code after an initial zero (the zero prefix selected trunk dialling) to form the first part of thesubscriber trunk dialling code for a region; the letters were followed by one or more digits. For example,Aylesbury was assigned 0AY6, which translated to 0296.
The letters have also been used, mainly in the United States, as a technique for remembering telephone numbers easily. For example, an interior decorator might license the telephone number 1-800-724-6837, but advertise it as the more memorablephoneword "1-800-PAINTER". Sometimes businesses advertise a number with a mnemonic word having more letters than there are digits in the phone number. Usually, this means that the caller just stops dialing at seven digits after the area code or that the extra digits are ignored by the telephone exchange.
In earlycell phones, orfeature phones, the letters on the keys are used for text entry tasks such astext messaging, entering names in the phone book, andbrowsing the web. To compensate for the smaller number of keys, phones usedmulti-tap and laterpredictive text processing to speed up the process.Touchscreen phones have made these input methods obsolete, as the screens are typically large enough to show as many virtual buttons as necessary for a full keyboard.
Pressing a single key of a traditional analog telephone keypad produces a telephony signaling event to the remote switching system. For touchtone service, the signal is adual-tone multi-frequency signaling tone consisting of two simultaneouspure tonesinusoidal frequencies. The row in which the key appears determines the low-frequency component, and the column determines the high-frequency component. For example, pressing key1 results in a signal composed of tones with frequencies 697hertz (Hz) and 1209 Hz.
| 1209 Hz | 1336 Hz | 1477 Hz | 1633 Hz | |
|---|---|---|---|---|
| 697 Hz | 1ⓘ | 2ⓘ | 3ⓘ | Aⓘ |
| 770 Hz | 4ⓘ | 5ⓘ | 6ⓘ | Bⓘ |
| 852 Hz | 7ⓘ | 8ⓘ | 9ⓘ | Cⓘ |
| 941 Hz | *ⓘ | 0ⓘ | #ⓘ | Dⓘ |
In the course oftelephone history, dials as well as keypads have been associated with various mappings of letters and characters to numbers.
The system used in Denmark[failed verification] was different from that used in the UK, which, in turn, was different from the US and Australia.[14] The use of alphanumeric codes forarea codes was abandoned in Europe when international direct dialing was introduced in the 1960s, because, for example, dialing VIC 8900 on a Danish telephone would result in a different number to dialling it on a British telephone. At the same time, letters were no longer placed on the dials/keypads of new telephones.
Letters did not reappear on phones in Europe until the introduction of mobile phones, and the layout followed the new international standardITU E.161/ISO 9995-8. The ITU established an international standard (ITU E.161) in the mid-1990s, recommended that this should be the layout used on any new devices.[15] There is a standard, ETSI ES 202 130, that covers European languages and other languages used in Europe, published by the independentETSI organisation in 2003[16] and updated in 2007.[17] Documentation describing some principles of the standard is available.[18]
Early smartphones such as thePalm Treo,HTC Wizard andBlackBerry had full alphanumeric keyboards instead of the traditional telephone keypads, and the user had to execute additional steps to dial a number containing convenience letters. On certain BlackBerry devices, a user can press theAlt key followed by the desired letter, and the device will generate the appropriate DTMF tone.[19]
Later smartphones moved toon-screen virtual keyboards and keypads. The latter typically include the ITU standard letters next to each number (and manyAndroid phone use the1 key to access voicemail and the zero to type a "+").
On the 4 × 3 array, the symbol on the button [...] should have a shape easily identified as the general shape shown in Figure 2. [...] The symbol will be known as thestar or the equivalent term in other languages.
