Instead of tapping the “4” key three times to input the letter “i” in a text message, with T9 you can just tap “4663” to spell the word “good”. With T9 active, you’d only have to tap each number once per letter. Most modern cell phones have T9 included and activated by default.
Hitting “7” four times to get the letter “s,” for example, was a multi-tap method used by older cell phones.
T9 is a patented technology that was originally developed by Tegic Communications, which is now part of Nuance Communications. T9 competes with Motorola’s iTap, RIM’s SureType as well as LetterWise and WordWise from Eatoni.
T9 is designed to get smarter based on the word uses of the user. When certain numbers are entered, T9 looks up words in its fast-access dictionary. When a numerical sequence could yield various words, T9 will display the word most commonly entered by the user.
If a new word is typed that’s not in the T9 dictionary, the software will add it to its predictive database so it will be displayed next time.
While T9 can learn based on user experiences, it doesn’t always correctly guess the word you intend. For example, “4663” could also spell “hood,” “home” and “gone”. When multiple words can be created by the same numeric sequence, they are called textonyms.
Some versions of T9 have smart punctuation. This allows the user to add word punctuation (i.e. the apostrophe in “didn’t”) and sentence punctuation (i.e. a period at the end of a sentence) using the “1” key.
T9 can even learn word pairs that you use often to predict the next word. For example, T9 could guess you’re going to type “home” after “go” if you use “go home” often.