Before touchscreens, every message went through twelve keys.
Each key holds three or four letters. Press it repeatedly to cycle through them, then wait — after about a second the letter is committed and the cursor moves on.
That pause is the part people forget. Typing two letters from the same key in a row — the c and a of “cab”, both on 2 — meant pressing 2 three times, waiting, then pressing it once more.
Press each key once per letter and a dictionary guesses the word. “Hello” is just 4-3-5-5-6.
Different words share a key sequence, so 4663 could be home, good, gone or hood. The phone offered the most common one first, and ✱ cycled to the next. Getting that order right is what separated a good T9 from an infuriating one.