Text on nine keys (T9) is a system that lets fixed and mobile phone users send text messages by pressing a number key for each letter in the message -- effectively making a keyboard out of the nine numeric phone entry keys. The system is already somewhat familiar to anyone who enters the letters of a name when checking a bank balance or looking up someone in a company's phone directory over the phone.
T9 was developed as a faster alternative to multi-tapping, a text input system that requires the user to tap a key from two to four times to select many letters. In contrast, T9 uses predictive software to enable identification of a letter with a single key tap.
Originated by Tegic Communications, the T9 system has been licensed for use by over 20 mobile phone manufacturers. T9 is often be used in combination with the Short Message Service (SMS) and the Wireless Application Protocol (WAP).