Although the majority of traffic accidents in the United States aren't linked to cellular phone use, it makes great sense to limit your conversations while driving a car anyway, and not only because of the destructive radiation these devices emit.
In fact, driving while using a hands-free cellular phone can make you just as prone to accidents as handheld phones due to a lack of focus on the primary task at hand, according to a new study of 500 adult drivers.
The key factor you need to know: Conversations in the car -- whether they're over the phone or in person -- are a distraction because they drain the average person's attention span.
And, because people are aware they're balancing two important things at once, they tend to drive and react to road conditions more slowly too (you've probably seen people in their 20s with reaction times comparable to seniors out on the road).
People also tend to forget what they see on the road if they've been yakking it up on the phone, especially if the topics shared are emotional ones.
All that said, probably the best thing you can do for your health in regard to cellular phones -- besides wearing a headset equipped with a ferrite bead that protects your head from radiation -- is to minimize your use.
Now having said all that, there is one possible exception. I picked a new car earlier this year that was equipped with Bluetooth (wireless) connection to my cell phone. When I enter the car it immediately recognizes the phone and syncs with it. So all I have to do is press a button on the steering wheel and talk and the microphone in the sun visor picks up my voice.
If a phone call comes in, the radio or CD player automatically shuts off so one can talk. It is almost like talking to someone in the other seat of the car and my guess is it poses about the same risk.
Not quite as amazing as GPS, but it is really amazing to me.