Editing Telephone keypad

{{Short description|Keypad that appears on some telephones}}
[[File:Telephone-keypad2.svg|thumb|right|200px|A telephone keypad using the ITU [[E.161]] standard.]]
A '''telephone keypad''' is a [[keypad]] installed on a [[push-button telephone]] or similar [[telecommunication]] device for dialing a [[telephone number]]. It was standardized when the [[dual-tone multi-frequency signaling]] (DTMF) system was developed in the [[Bell System]] in the United States in the 1960s&nbsp;– this replaced [[rotary dial]]ing, that had been developed for electromechanical telephone switching systems.<ref name="Engineering Pathway">{{cite web|url=http://www.k-grayengineeringeducation.com/blog/index.php/2009/11/18/engineering-education-today-in-history-blog-bell-telephone-introduces-push-button-telephone-2/|title=Engineering Education "Today in History" Blog: Bell Telephone introduces push button telephone|last=Agogino|first=Alice|date=November 18, 2009|website=Engineering Pathway|archive-url=https://archive.today/20130127020012/http://www.k-grayengineeringeducation.com/blog/index.php/2009/11/18/engineering-education-today-in-history-blog-bell-telephone-introduces-push-button-telephone-2/|archive-date=January 27, 2013|url-status=dead}}</ref> 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 of [[John Karlin]] at the Human Factors Engineering Department of [[Bell Labs]].<ref>B.L. Hanson, ''A Brief History of Applied Behavioral Science at Bell Laboratories'', Bell System Technical Journal 62(6) 1571–1590 (July–August 1983), p.1578</ref><ref name="deininger" /> 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 the [[Autovon]] 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 labelled [[asterisk|star]], {{Keypress|✻}}, and [[number sign|number sign/hash]], {{Keypress|#}}, 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 in [[vertical service code|Custom Calling Services]] (CLASS) features installed in [[electronic switching system]]s.<ref>D.P. Worrall, ''New Custom Calling Services'', Bell System Technical Journal 61(5) 821–839 (May–June 1982)</ref>

==Layout==
[[File:Phone from 1950s uk - This one is real.JPG|thumb|Telephone with letters on its rotary dial (1950s, UK)]] 
The layout of the digit keys is different from that commonly appearing on [[calculator]]s and [[numeric keypad]]s. This layout was chosen after extensive [[human factors]] testing at Bell Labs.<ref name=deininger>{{cite journal | title=Human Factors Engineering Studies of the Design and Use of Pushbutton Telephone Sets | last=Deininger | first=R. L. | date=1960-02-16 | journal=Bell System Technical Journal | volume=39 | issue=4 | pages=995–1012 | doi=10.1002/j.1538-7305.1960.tb04447.x }}</ref><ref name="expectedLocations">{{cite journal | title=Expected Locations of Digits and Letters on Ten-Button Keysets | last1=Lutz | first1=Mary Champion | last2=Chapanis | first2=Alphonse | journal=Journal of Applied Psychology | volume=39 | issue=5 | pages=314–317 | date=October 1955 | doi=10.1037/h0048722}}</ref> At the time (late 1950s), mechanical calculators were not widespread, and few people had experience with them.<ref>{{cite AV media | people=Brady Haran (producer), Sarah Wiseman (interviewee) | date=2013-08-29 | title=Phone Numbers - Numberphile | url=https://www.youtube.com/watch?v=kCSzjExvbTQ  |archive-url=https://ghostarchive.org/varchive/youtube/20211212/kCSzjExvbTQ| archive-date=2021-12-12 |url-status=live| access-date=2016-05-11}}{{cbignore}}</ref> 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."<ref name="expectedLocations"/> Meanwhile, a 1960 paper&nbsp;– just five years later&nbsp;– refers to today's common calculator layout as "the arrangement frequently found in ten-key adding machines".<ref name=deininger /> 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.

[[File:GPO 726 Phone.jpg|thumb|British [[GPO telephones#Type 726|GPO 726 telephone]] of 1967]]The key labeled {{Keypress|✻}} was officially named the "star" key. The key labeled {{Keypress|#}} is officially called the "[[number sign]]" key, but other names such as "pound", "hash", "hex", "[[octothorpe]]", "gate", "lattice", and "square" are common, depending on national or personal preference. The Greek symbols ''[[alpha]]'' and ''[[omega]]'' had been planned originally.<ref>Koten, John F., " '''*#''' ", ''WSJ.Money Magazine'', Issue 5, p. 22 (Spring 2014). The star and number sign were likely first suggested by John A. "Jack" Koten (1929-2014), a corporate communications specialist with [[Bell Labs]] in Chicago, reasoning that the new keys would be easier to explain to a public already familiar with typewriter symbols.</ref>

These can be used for [[Vertical service code|special functions]]. For example, in the UK, users can order a 7:30{{nbsp}}am alarm call from a [[BT Group|BT]] [[telephone exchange]] by dialing: '''✻55✻0730#'''.<ref>{{Cite web |title=Reminder Call Instructions &#124; BT Business |url=http://btbusiness.custhelp.com/app/answers/detail/a_id/7698/~/reminder-call-instructions}}</ref>

In the Americas and a number of other countries, most dials and, later, keypads also bear letters according to the following system:[[File:Telephone keys.JPG|right|thumb|A standard telephone keypad]]
{{Table alignment}}

{| class="wikitable defaultleft col1center"
|-
!Key !! Letters
|-
|{{Keypress|1}} || none (on some older telephones, QZ)
|-
|{{Keypress|2}} || ABC
|-
|{{Keypress|3}} || DEF
|-
|{{Keypress|4}} || GHI
|-
|{{Keypress|5}} || JKL
|-
|{{Keypress|6}} || MNO (on some older telephones, MN)
|-
|{{Keypress|7}} || PQRS (on older telephones, PRS)
|-
|{{Keypress|8}} || TUV
|-
|{{Keypress|9}} || WXYZ (on older telephones, WXY)
|-
|{{Keypress|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:

{{Table alignment}}

{| class="wikitable defaultcenter"
|-
!Key !! Letters
|-
|{{Keypress|1}} || none
|-
|{{Keypress|2}} || ABC
|-
|{{Keypress|3}} || DEF
|-
|{{Keypress|4}} || GHI
|-
|{{Keypress|5}} || JKL
|-
|{{Keypress|6}} || MN

|-

|{{Keypress|7}} || PRS
|-
|{{Keypress|8}} || TUV
|-
|{{Keypress|9}} || WXY

|-

|{{Keypress|0}} || OQ
|}
Putting the letter O on the zero makes sense, as in British speech, "oh" is often said rather than "nought" or "zero"; Q is visually similar to O, and therefore the two might be confused. Therefore, two possible mistakes were avoided.

These letter assignments have been used for multiple purposes. Originally, they referred to the leading letters of [[telephone exchange names]]. In the mid-20th century United States, before the switch to [[All-Number Calling]], telephone numbers had seven digits, including a two-digit prefix which was expressed in letters rather than digits, e.g.; [[Telephone number#US phone number history|KL5-5445]]. The [[Telephone numbers in the United Kingdom|UK 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 the [[subscriber 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.

[[File:MUTCD-CA S32.svg|thumb|right|The official toll-free hotline for the [[California Department of Transportation]]'s [[Adopt-a-Highway]] program is 1-866-236-7824, but signs advertise the number as 1-866-ADOPTAHWY, with two extra digits, for memorability.]]

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 memorable [[phoneword]] "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 early [[Cell phone|cell phones]], or [[feature phone]]s, the letters on the keys are used for text entry tasks such as [[text messaging]], entering names in the phone book, and [[Mobile web browser|browsing the web]]. To compensate for the smaller number of keys, phones used [[multi-tap]] and later [[predictive 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.

==Key tones==
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 a [[dual-tone multi-frequency signaling]] tone consisting of two simultaneous [[pure tone]] [[Sine wave|sinusoid]]al frequencies. The row in which the key appears determines the low-frequency component, and the column determines the high-frequency component. For example, pressing key ''1'' results in a signal composed of tones with frequencies 697 [[hertz]] (Hz) and 1209&nbsp;Hz.

{| class="wikitable"
|+ DTMF keypad frequencies (with sound clips)<ref name="lancaster" >Don Lancaster. [https://www.tinaja.com/ebooks/tvtcb.pdf "TV Typewriter Cookbook"]. ([[TV Typewriter]]). Section "400-Style (Touch-Tone) Modems". p. 177-178.</ref>
|-
!align=center|
!align=center| 1209&nbsp;Hz
!align=center| 1336&nbsp;Hz
!align=center| 1477&nbsp;Hz
!align=center| 1633&nbsp;Hz
|-
!align=center| 697&nbsp;Hz
|align=center| {{Audio|Dtmf1.ogg|1}}
|align=center| {{Audio|Dtmf2.ogg|2}}
|align=center| {{Audio|Dtmf3.ogg|3}}
|align=center| {{Audio|DtmfA.ogg|A}}
|-
!align=center| 770&nbsp;Hz
|align=center| {{Audio|Dtmf4.ogg|4}}
|align=center| {{Audio|Dtmf5.ogg|5}}
|align=center| {{Audio|Dtmf6.ogg|6}}
|align=center| {{Audio|DtmfB.ogg|B}}
|-
!align=center| 852&nbsp;Hz
|align=center| {{Audio|Dtmf7.ogg|7}}
|align=center| {{Audio|Dtmf8.ogg|8}}
|align=center| {{Audio|Dtmf9.ogg|9}}
|align=center| {{Audio|DtmfC.ogg|C}}
|-
!align=center| 941&nbsp;Hz
|align=center| {{Audio|DtmfStar.ogg|&ast;}}
|align=center| {{Audio|Dtmf0.ogg| 0}}
|align=center| {{Audio|DtmfPound.oga|&num;}}
|align=center| {{Audio|DtmfD.ogg|D}}
|}

==Letter mapping==

[[File:Japanese mobile phone keypad.jpg|thumb|A mobile phone keypad with Latin and Japanese characters.]]

In the course of [[history of the telephone|telephone 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|date=August 2014}} was different from that used in the UK, which, in turn, was different from the US and Australia.<ref>[http://www.dialabc.com/motion/keypads.html Phone Key Pads<!-- Bot generated title -->] {{Webarchive|url=https://web.archive.org/web/20150315022743/http://dialabc.com/motion/keypads.html |date=2015-03-15 }}</ref> The use of alphanumeric codes for [[Telephone numbering plan#Area code|area 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 standard [[E.161|ITU E.161]]/[[ISO/IEC 9995|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.<ref>[http://www.itu.int/rec/T-REC-E.161-200102-I/en E.161 : Arrangement of digits, letters and symbols on telephones and other devices that can be used for gaining access to a telephone network<!-- Bot generated title -->]</ref> There is a standard, ETSI ES 202 130, that covers European languages and other languages used in Europe, published by the independent [[ETSI]] organisation in 2003<ref name="etsi00">{{Citation
| publisher = ETSI
| last = ETSI
| title = ETSI ES 202 130 Ver. 1.1.1: Human Factors (HF); User Interfaces; Character repertoires, ordering rules and assignments to the 12-key telephone keypad
| access-date = 2011-11-03
| date = 2003-10-29
| url = http://webapp.etsi.org/WorkProgram/Report_WorkItem.asp?WKI_ID=11730
}}
</ref> and updated in 2007.<ref name="etsi07">{{Citation
| publisher = ETSI
| last = ETSI
| title = ETSI ES 202 130 Ver. 2.1.2: Human Factors (HF); User Interfaces; Character repertoires, orderings and assignments to the 12-key telephone keypad (for European languages and other languages used in Europe)
| date = 2007-09-06
| url = http://webapp.etsi.org/WorkProgram/Report_WorkItem.asp?WKI_ID=11730
}}
</ref> Documentation describing some principles of the standard is available.<ref name="Boecker06">{{Citation
| doi = 10.1145/1151314.1151336
| issn = 1072-5520
| volume = 13
| pages = 30
| last1 = Böcker
| first1 = Martin
| first2 = Bruno 
| last2 = von Niman
| first3 = Karl Ivar
| last3 = Larsson
| title = Increasing text-entry usability in mobile devices for languages used in Europe
| journal = Interactions
| date = 2006-09-01
| citeseerx = 10.1.1.125.7511
| issue = 5
| s2cid = 20736144
}}
</ref>

Early smartphones such as the [[Palm Treo]], [[HTC Wizard]] and [[BlackBerry]] 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 the {{Keypress|Alt}} key followed by the desired letter, and the device will generate the appropriate DTMF tone.<ref>[http://www.pctoday.com/editorial/article.asp?article=articles%2F2005%2Ft0310%2F35t10%2F35t10.asp Blackberry Tips], ''PC World'', October 2005.</ref>

Later smartphones moved to [[Virtual keyboard|on-screen virtual keyboards and keypads]]. The latter typically include the ITU standard letters next to each number (and many [[Android (operating system)|Android]] phone use the {{Keypress|1}} key to access voicemail and the zero to type a "+").

==See also==
{{Commonscat|Telephone keypads}}
{{Portal|Telephones}}
* [[E.161]]
* [[Phoneword]]
* [[Rotary dial]]
* [[T9 (predictive text)|T9]]

{{-}}

==References==
{{reflist|2}}

[[Category:Telephony equipment]]
[[Category:Telephone numbers]]