They are distinctly different from words which interchange simply due to a typo and auto incorrect.
Guy in text back: Hoof night! Knud you tom!
Girl in text: Oh T9onyms! Like a secret code! You're so funny!
Mom in text: When will you be good?
Son in text: What? ...Always?
Mom in text: Don't tall back! Bond gone nox!
Son in text: I think you are having a T9onym attack...