T9, which stands for Text on 9 keys, is a patented[1] predictive text technology for mobile phones, originally developed by Tegic Communications, now part of Nuance Communications[2]. Read more on Wikipedia
This is usually used in mobile phones for predictive alphabet input. Each key have associated letters, such as 2 for ABC, 3 for DEF, and so on… This function allow you to search combination from entered number, for example, input 23 will return ad, ae, af, bd, be, bf, cd, ce and cf, in array.
