What’s the deal with T9?

T9 stands for "Text on 9 Keys". It is a system designed to increase the speed of sending text messages, by reverse converting the number keys into words using the letter components of the keys.

It uses the same system used now to spell out words, such as 1-800-GEE-KSQUA converting to 1-800-433-5778, or in the days of telephone operators where PennsylvniA 6-5000 became 726-5000. As you type in single numbers that standard for one of 3 or 4 letters, it cross references that with a dictionary of words to find out what word you may be typing. It is not flawless, because there are a number of words that are spelled by the same four numbers (for example, 5646 spells both “join” and “logo”), however most systems will present the most common word, and then offer you a chance to pick other options. However the benefit is that instead of using non-T9 text messaging systems where you would have to hit the 5 key three times to move from “j” to “k” to “l”, you can just hit the 5 key once and it figures out from context which letter it should be.