Not too long back I had a guy come out at a stop sign when I was turning left in front of him. He was juggling a cell phone in one hand and a drink cup in the other. When he realized that I wasn't gonna stop so he could cut me off, he had to jam on his brakes. Cell phone one way - drink another, and the whole time he's hollering at me and waving his fists.
As soon as I cleared the corner, I stopped in his lane and stepped out of the car waiting for him. He quickly realized the error of his ways and just waved 'bye' to me and stayed in his vehicle.
The problem wasn't the cell phone or the drink. . . it was that his MIND was not on his driving. And that's what cell phone usage (and changing CD, reading a book - yeah, I've seen that) does to drivers - diverts the attention that they should be devoting to driving elsewhere.
To me, the ideal cell phone for a car would be the one that shuts down the ignition when you turn it on.

You wanna talk on the phone in a car, pull over and devote your full attention to talking.