Tbh I could do that on a plain numeric keypad. I remember blindly texting under my desk in school. I wouldn't be able to do it nowadays though.

The first versions of t9 were entirely predictable and hardcoded so the words were always in the same order when pressing star. Later versions had some optimisations that mad it change, but it settled quite quickly to your writing style. I'm always surprised how few countries adopted t9... I'd Denmark literally everyone used t9. Even my mom. And you were weird if not using it. It wa also stupid fast to type on.