I think that if you can't prove impairment, if the driver isn't driving erratically or otherwise breaking real traffic laws, or endangering themselves or others, then no crime has been committed. Yes, distracted drivers are bad, no i don't feel that a hands free set is distracting, unless we're also going to ban anyone from speaking to the driver entirely.
Yes, I think that hands-free cell phone usage while driving should be legal, because it is similar to just talking to someone who is in their car. The harm and risk that comes with talking on a hands-free phone is minimal. The person still has two hands to react to problems on the road.
Hands-free cell phone usage while driving should be legal. It would be very difficult to pass a law that says hands-free cell phone usage is illegal. If that is illegal, talking to your friends or children in the car would be illegal, too. Although it's not a good idea to drive distracted, there is no way to mandate no talking in the car.
I do not believe hands-free cell phone usage should be allowed while driving. I think the use of these devices is still too much for those that are behind the wheel. Driving is a serious matter that requires a lot of attention. We do not need any more accidents that involve cell phone usage.