Lazs is right, in that the real danger is not holding the phone, it's any form of distracted driving that's dangerous. I read somewhere that talking on the phone, or searching tracks on the CD player, or whatever...reduces driving response time to that of a person in their 70's.
'Hands-free' legislation just garners the dumb-arse votes for short-sighted, ill-informed politicians. It doesn't make us safer.
Distracted driving laws...maybe...