Vocal recognition software was good enough to pick up numbers and lightweight enough to fit on a phone of that size in 1988?
I remember my dad purchasing a speech recognition package in the early 90s, but it ran on an expensive 486 desktop machine and was reasonably but not accurate enough for his uses.
https://en.wikipedia.org/wiki/Apricot_Portable https://www.youtube.com/watch?v=ewu_NBUHePU