How about some common sense?
I remember the first ticket against Illinois' no texting law January 2011. Middle of the night a cop pulled over a driver first for improper lane use. Then the cop saw he was texting. It didn't take long for the cop to notice the driver was hammered. And then no license because it was revoked for multiple previous DUIs. And then no insurance (required in IL) because his license was revoked. Was the no texting law necessary for that arrest?
I've evaded crashes from drivers not paying attention to the road while carrying on animated conversations with front seat passengers, and worse, mothers ignoring the road while yelling at and looking at their kids in the back seat. Should there be a no talking law? A no looking back law? How can you tell if a driver is looking at her kids in the back seat or looking out a rear window to see what's in the next lane or behind her?
I once had a near miss from a guy eating soup with a spoon while driving. And I've lost count of the number of people I've seen using the rear view mirror to do makeup with the right hand and smoking a cigarette held in the left.
On the other hand, yakking on the phone while cruising light traffic roads helps keep me more alert than just staring out the windshield and being hypnotized by the same scenery and passively listening to the radio or iPod.
It's impossible to list all possible stupid things drivers do, and a no cell phone law is a good example of unenforceable overkill letting most violators go unhindered while the few stops for cell phone use would most likely nail drivers doing nothing unsafe.
The states probably already have distracted driving laws. Do we need a law explicitly prohibiting smoking a cigarette while working on makeup in the rear view mirror, or should we trust police to stop and judges to convict for dangerous behavior in a moving vehicle? Why should stupid phone or iPod use be any different?