T9 (predictive text)

T9 ("Text on 9 keys") is the predictive-text system that made keypad texting fast: instead of multi-tapping (press 7 four times for "s"), you press each digit once and T9 guesses the intended word from its dictionary — "43556" becomes "hello."

Anyone who texted in the 2000s has T9 muscle memory that returns within days. Modern dumbphones still ship it, and some (Sunbeam, Schok) supplement it with voice dictation. Texting on T9 is deliberate rather than effortless — many switchers count that friction as a feature: messages get shorter, calls get longer.