I think cell phone use (whether for chatting or -- heaven forfend -- texting) while driving should be banned. Seriously.
Why? Allow me to illustrate with a little people-watching exercise.
I work in downtown Des Moines, which is connected by a fairly extensive skywalk system. In effect, it's an elevated ant farm for corporate cubicle drones like myself. At about noon every day, several massive companies disgorge their hordes of employees into this network of glorified hallways for lunch, and many of those employees immediately take up their personal cell phones for a chat or a text.
And I've noticed that when people are using their phones for whatever purpose, they are ENTIRELY INCAPABLE OF WALKING IN A STRAIGHT LINE AT A NORMAL SPEED. Watch for yourself sometime. If you're in a large crowd where a lot of people are using phones, chances are you'll get a full-body check (or at least a near miss) from one of these distracted walkers.
Knowing those odds, I don't think I'm being unreasonable to expect that these same people should NOT operate a half-ton of horsepower while using their phones. The full-body check on foot isn't so bad; heck, if you're paying attention, you can plant your feet and "accidentally" put someone on their tuchus (not that I would do such a thing, of course). But if I'm on the bike and that person is doing S-curves down a straight road in a friggin' Hummer while tapping out OMGs and LOLs, I'm toast.
(Hypocrite alert: I will sometimes answer my phone while riding the bike. You may fling rotten virtual tomatoes at me now.)