T9 (predictive text)

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T9, which stands for Text on 9 keys, is a predictive text technology for mobile phones, developed by Tegic Communications. It is used on phones from LG, Samsung, Nokia, Siemens, Sony Ericsson, Sanyo, and others. Its main competitors are iTap, created by Motorola, and LetterWise, created by Eatoni.

T9's objective is to make it easier to type text messages on small mobile devices. The technology allows words to be entered by a single keypress for each letter, as opposed to the approach used in the older generation of mobile phones in which several letters are associated with each key, and selecting one letter often requires multiple keypresses.

The software combines the groups of letters found on each phone key with a fast-access dictionary of words. It looks up all the possible words corresponding to the sequence of keypresses in the dictionary.

As the predictive software gains familiarity with the words and phrases the user commonly uses, it speeds the process by offering the most frequently used words first and then lets the user access other choices with one or more presses of a predefined NEXT key.

The Tegic Communications website offers training tools and web games such as this crossword puzzle [1] that are designed to help users become proficient with this interface.

The dictionary can be expanded by adding missing words, enabling software to recognize them in the future. After introducing a new word, the next time the user tries to produce that word T9 will add it to the predictive dictionary.

[edit] Interface workflow

Enter a word by tapping one key per letter.
The word displayed on the screen is not valid until the whole text is typed. Since T9 tries to find matching words while typing, the suggested word may change after each key press.
If T9 displays a word that is not the one you are looking for, press the NEXT key to scroll through the possible matches.
If the wanted word is not in T9’s dictionary, there's an option to add it after visiting all available words with the NEXT key. The word must be typed with the traditional multi-tap method.