Telephone Keypad - Letter Mapping

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) on telephone keypads over the years.

The system used in Denmark was different from that used in the U.K., 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 VIC 8900 on a Danish telephone would result in a different number than dialling it on a British telephone. 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 / ISO 9995-8.

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 and BlackBerry) 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 (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.