T9

T9 is a predictive text input method often used for Short message service(SMS) mobile phone text messages. This method attempts to improve on the common multi-tap method by requiring fewer total button taps. It achieves this by using a small, quick-access dictionary to automatically display the word most often desired for a sequence of keystrokes.

The layout for an ITU-T E.161 standard keypad.

1	2 ABC	3 DEF
4 GHI	5 JKL	6 MNO
7 PQRS	8 TUV	9 WXYZ
*	0	#

For example, a user desiring to input the word "the" would press the buttons containing each letter; 'T' on the 8 button, 'H' on the 4 button, and 'E' on the 3 button. The computer receives the input 8-4-3 and accesses its database to determine what word is most frequently associated with that sequence. In this case "the" is most common, and thus appears immediately. When the most common word is not the desired word, there is a button that cycles the database to the next most common word, and so on until the desired word appears. In the above example, the T9 method uses 3 total keystrokes compared to 5 using the multi-tap method.