Many phones have a little dimple so you can easily find 5 on the keypad. But touch texting can be a little hard, when you don't have any feedback as to what you're putting in.
So, feedback mechanisms to enable this:
*Simple vibrate tones could let you know whether you have a dictionary word or
not.
*Vibrating morse code could feed back to you in plain text what you wrote.
*If you have headphones on, it could just read you your message as you type it in.
This would be great for taking notes as you wander around, or for surreptitiously taking notes.