Risk of using a phone while driving isn't easy to pin down.

Simulations suggest that drivers don't perform as well while talking on the phone or doing any other extraneous task. But isolating the effects of cell phone use is difficult. It is not known if the type of crashes varies, i.e., more fender-benders versus more injury crashes. Also needed is data on cell phone use by drivers who do not get in crashes. (Author/publisher)