Telephone keypad - AbsoluteAstronomy.com

A telephone keypad is a keypad

Keypad

A keypad is a set of buttons arranged in a block or "pad" which usually bear digits, symbols and usually a complete set of alphabetical letters. If it mostly contains numbers then it can also be called a numeric keypad...

that appears on a "Touch Tone" telephone

Telephone

The telephone , colloquially referred to as a phone, is a telecommunications device that transmits and receives sounds, usually the human voice. Telephones are a point-to-point communication system whose most basic function is to allow two people separated by large distances to talk to each other...

. It was standardised when the dual-tone multi-frequency

Dual-tone multi-frequency

Dual-tone multi-frequency signaling is used for telecommunication signaling over analog telephone lines in the voice-frequency band between telephone handsets and other communications devices and the switching center. The version of DTMF that is used in push-button telephones for tone dialing is...

system in the new push-button telephone

Push-button telephone

The push-button telephone was first invented in 1941, and is a telephone with push-buttons or keys, and which eventually replaced rotary dial telephones that were first used in 1891. The first push-button telephone was invented in the labs of Bell Telephone; however, these models were only...

was introduced in the 1960s, which gradually replaced the rotary dial

Rotary dial

The rotary dial is a device mounted on or in a telephone or switchboard that is designed to send electrical pulses, known as pulse dialing, corresponding to the number dialed. The early form of the rotary dial used lugs on a finger plate instead of holes. Almon Brown Strowger filed the first patent...

.

The contemporary keypad is laid out in a 4×3 grid, although the original DTMF

Dual-tone multi-frequency

system in the new keypad had an additional column for four now-defunct menu selector keys. When used to dial a telephone number, pressing a single key will produce a pitch

Pitch (music)

Pitch is an auditory perceptual property that allows the ordering of sounds on a frequency-related scale.Pitches are compared as "higher" and "lower" in the sense associated with musical melodies,...

consisting of two simultaneous pure tone

Pure tone

A pure tone is a tone with a sinusoidal waveshape.A sine wave is characterized by its frequency, the number of cycles per second—or its wavelength, the distance the waveform travels through its medium within a period—and the amplitude, the size of each cycle...

sinusoidal frequencies. The row in which the key appears determines the low frequency, and the column determines the high frequency. For example, pressing the '1' key will result in a sound composed of both a 697 and a 1209 hertz

Hertz

The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications....

(Hz) tone.

DTMF Keypad Frequencies (with sound clips)
1209 Hz	1336 Hz	1477 Hz
1	2	3	697 Hz
4	5	6	770 Hz
7	8	9	852 Hz
*	0	#	941 Hz

Note that the layout of the digits is different from that commonly appearing on calculator

Calculator

An electronic calculator is a small, portable, usually inexpensive electronic device used to perform the basic operations of arithmetic. Modern calculators are more portable than most computers, though most PDAs are comparable in size to handheld calculators.The first solid-state electronic...

s and numeric keypad

Numeric keypad

A numeric keypad, numpad or tenkey for short, is the small, palm-sized, seventeen key section of a computer keyboard, usually on the very far right. The numeric keypad features digits 0 to 9, addition , subtraction , multiplication and division symbols, a decimal point and Num Lock and Enter keys...

s.

The "*" is called the "star key" or "asterisk

Asterisk

An asterisk is a typographical symbol or glyph. It is so called because it resembles a conventional image of a star. Computer scientists and mathematicians often pronounce it as star...

key". "#" is called the "number sign

Number sign

Number sign is a name for the symbol #, which is used for a variety of purposes including, in some countries, the designation of a number...

", "pound key", or "hash key", depending on one's nationality or personal preference. These can be used for special functions. For example, in the UK, users can order a 7.30am alarm call from a British Telecom telephone exchange

Telephone exchange

In the field of telecommunications, a telephone exchange or telephone switch is a system of electronic components that connects telephone calls...

by dialling: *55*0730#.

Most of the keys also bear letters according to the following system:

0 = none (in some telephones, "OPERATOR" or "OPER")

1 = none (in some older telephones, QZ)

2 = ABC

3 = DEF

4 = GHI

5 = JKL

6 = MNO

7 = P(Q)RS

8 = TUV

9 = WXY(Z)

These letters have had several auxiliary uses. Originally, they referred to exchange

Telephone exchange names

During the early years of telephone service, communities that required more than 10,000 telephone numbers, whether dial service was available or not, utilized exchange names to distinguish identical numerics for different customers....

s. In the mid-20th century United States, before the advent of All-Number Calling

All-Number Calling

All-number calling is a telephone numbering system that was introduced in the United States in the 1960s and 1970s.Until the 1950s, local telephone numbers consisted of an exchange and a 5-digit phone number...

, numbers were seven digits long including a two-digit prefix which was expressed as the letters rather than numbers e.g.; KLondike5-5445. The UK telephone numbering system

UK telephone numbering plan

The UK telephone numbering plan, also known as the National Telephone Numbering Plan, is the system used for assigning telephone numbers in the United Kingdom and the Crown Dependencies...

used a similar two-letter code after the initial zero to form the first part of the subscriber trunk dialling

Subscriber trunk dialling

Subscriber trunk dialling is a term for a telephone system allowing subscribers to dial trunk calls without operator assistance.- Terminology :...

code for that region - for example, Aylesbury

Aylesbury

Aylesbury is the county town of Buckinghamshire in South East England. However the town also falls into a geographical region known as the South Midlands an area that ecompasses the north of the South East, and the southern extremities of the East Midlands...

was assigned 0AY6 which translated into 0296. (The majority of these original numbers have remained, particularly in the rural areas, and are currently still in service. The modern equivalent of 0AY6, namely 01296, still refers to Aylesbury.)

The letters have also been used, mainly in the United States, as a way of remembering telephone numbers easily. For example, an interior decorator might license the phone number 1-800-724-6837 but advertise it as the more memorable phoneword

Phoneword

Phonewords are alphanumeric equivalents of a telephone number. In many countries, there exist letters corresponding to each digit on a telephone keypad...

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 you just stop dialing at 7 digits after the area code or that the numbers are ignored by the switchboard.

In recent times, the letters on the keys are needed also for entering text on mobile phone

Mobile phone

A mobile phone is a device which can make and receive telephone calls over a radio link whilst moving around a wide geographic area. It does so by connecting to a cellular network provided by a mobile network operator...

s, for text messaging

Text messaging

Text messaging, or texting, refers to the exchange of brief written text messages between fixed-line phone or mobile phone and fixed or portable devices over a network...

, entering names in the phone book, etc.; multi-tap

Multi-tap

Multi-tap refers to a text entry system for mobile phones.The alphabet is printed under each key in a three-letter sequence as follows; ABC under 2 key, DEF under 3 key, etc. Exceptions are the "7" key, which adds a letter , and the "9" key which includes "Z"...

and predictive text

Predictive text

Predictive text is an input technology used where one key or button represents many letters, such as on mobile phones and in accessibility technologies. Each key press results in a prediction rather than repeatedly sequencing through the same group of "letters" it represents, in the same,...

systems are used.

Letter mapping

When designing or selecting a new phone, publishing or using phonewords, one should be aware that there have been multiple standards for the mapping of letters (characters) to numbers (keypad layouts, as with keyboard layout

Keyboard layout

A keyboard layout is any specific mechanical, visual, or functional arrangement of the keys, legends, or key–meaning associations of a computer, typewriter, or other typographic keyboard....

) on telephone keypads over the years.

The system used in the UK was different from that used in France which was different from the U.S. etc. The use of alphanumeric codes for exchanges was abandoned in Europe when international direct dialling was introduced in the 1960s, because (for example) dialling WHI 1212 on a French phone would get different numbers to dialling it on a British phone. At the same time letters were no longer put on the dials of new telephones.

Letters did not re-appear on phones in Europe until the introduction of mobile phones, and the layout followed the new international standard ITU E.161

E.161

E.161 is an ITU-T recommendation that defines the assignment of the basic 26 Latin letters to the 12-key telephone keypad. Uses for this mapping include:* Multi-tap and predictive text systems* Forming phonewords from telephone numbers...

/ ISO 9995-8

ISO/IEC 9995

ISO/IEC 9995 Information technology — Keyboard layouts for text and office systems is an ISO standard defining layouts of computer keyboards. It defines a keyboard as having three groups of key assignments:...

.

The keypad pictured above is mapped according to the current international standard. The ITU established an international standard (ITU E.161) in the mid-1990s, and that should be the layout used for any new devices.

There is a standard that covers European languages and other languages used in Europe, published by independent ETSI organisation: ETSI ES 202 130; first published in 2003 and updated in 2007. (Work describing some principles of the standard is available
.)

Since many newer smartphones (such as PalmPilot

PalmPilot

The PalmPilot Personal and PalmPilot Professional are the second generation of Palm PDA devices produced by Palm Inc...

and BlackBerry

BlackBerry

BlackBerry is a line of mobile email and smartphone devices developed and designed by Canadian company Research In Motion since 1999.BlackBerry devices are smartphones, designed to function as personal digital assistants, portable media players, internet browsers, gaming devices, and much more...

) have full keyboards instead of the traditional telephone keypads, the user must execute additional steps to dial a number containing convenience letters. On certain BlackBerry devices, a user can press the Alt key, followed by the desired letter, and the device will generate the appropriate DTMF tone.

The first telephony application that did not deploy a dial pad is Blink

Blink (software)

Blink is a SIP client. Blink is distributed as free software under version 3 of the GPL license.The application is written in Python and Cocoa, a Qt port for Windows and Linux is also available...

(a screenshot of the pad-less audio interface is available here). As computers benefit of a full keyboard, the developers felt that it was more natural to allow typing DTMF tones by using the computer keyboard while in a middle of an audio session without having to present the end-user an explicit dial-pad graphical user interface.

Letter mapping

See also