T9

T9 (Text on 9 Keys) is a dictionary-based predictive text-entry method developed by Tegic Communications in the 1990s for mobile phone keypads with multiple letters assigned to each numeric key. Rather than pressing a key multiple times to cycle through letters (the older 'multi-tap' approach), the user presses each key once for the intended letter and a background dictionary disambiguates the sequence into the likely word. T9 was a major accessibility advance for users with motor impairments because it dramatically reduced required keystrokes; it was also a representative early example of the more general technique of Dictionary-based Predictive Disambiguation (DBPD), which underlies modern soft-keyboard autocorrect, swipe input, and AAC word-prediction systems.