You can now use a T9 keyboard on iOS, just like you always wanted
Text Message Using T9Word: Quickstart Guide, iPhone, & Android
Tappy: Android T9 Keyboard
T9 typing on Apple Watch | MacRumors Forums
Type Nine - The ultimate t9 style iOS keyboard
T9 Keyboard Manual - Michał Jankowski
I've never used a T9 keyboard before, so I'm learning it on my iPhone before I switch to a Nokia later next month. That way, I can utilize typing tests easier :
Old T9 Keyboard for Android - Download
How to: use T9-style keypad input on Belle Feature Pack 2