Just watched a 'mythbusters' TV program about hand held vs hands free phones. They did proper tests on a university driving simulator with eye movement sensors and a satnav in the car and someone phoning them, did it with 30 different drivers. All 30 drivers tested on hand held and hands free. Well results were pretty much identical, on an empty or low traffic highway they all coped fairly well with no drama, but as soon as they entered traffic or a built up area the fun started. Only 1 driver 'passed' the test (passed because they did not make a major mistake or have a crash). In both tests about 8 missed the satnav instructions and made a wrong turn, a lot of the rest either knocked someone off a bike or had a major crash (and only the one that passed had the expected attention rate for driving, the rest were 'inattentive' ) - the eye movement sensors clearly showed the drivers looking at the 'wrong' things when on the phone, and tended to wander across the road.
Conclusion was, hands free no better than hand held in the safety area, it may be more convenient but just as dangerous. This is not the first study to come to same conclusion.