Number Keypad for Text messages

How can I change the qwerty pad for a T9 numberpad like in other cell phones to make text messages? I only have one arm and it is very difficult to use the qwerty pad. Did apple ever thought of disable consumers? The T9 numpad for SMS messages is easier for disable people like me. There should be an option in the System Preferences to change the type of keypad between Qwerty and T9 Numpad.