Think you misunderstand me. Long before texting was a thing, landline phones (with rotary dials!) also had letters associated with digits. This layout was later transferred to keypads, which in turn became the SMS layout.

I bet this is also why old-timey phone numbers encoded the first digits with letters. The US had the famous ABC2/DEF3/… system that’s still displayed on most keypads, and the former Soviet Union mapped the first letters of the Russian alphabet (skipping З to avoid confusion with 3)…