if you're driving with an iPhone... you might wan make sure you have a passenger keeping an eye on the road for you...
what's good about the keys (on any phone) is that you can actually FEEL them. if you can memorize where each key is (or just the number keys), you'll be able to dial a number while keeping an eye on the road. if you get a wrong number, no problem: just hang up and dial again. you'll still be safer.
i used to use a nokia 7710 (touchscreen). dialing on that was a b & a half. only time i could dial was if i was stuck @ a red light or pulled over. other than that, if i tried to dial while driving, i'd keep having to stare and the screen & sometimes i'd miss... then i'd have to look for the "delete/back" button.
that's my 2 cents.