The sooner it's implemented here the better. Many many investigations over the past few years have shown talking on the phone to increase the likelyhood of accidents. Do a search at New Scientist and you'll find many articles including...
"Hands-free cellphones carry car crash risk too"
"Hands-free phones not risk-free for drivers"
"Hands-free kits do not reduce crash risk"
"Cellphones worse than drink-driving"
Not policeable? I don't think that's an issue.
Car's fitted with handsfree should fail MOT's.
Any car with a live phone in it could automatically detected by roadside or mobile detectors and be subject to an automated fine system. (yeah so passengers can't use them either - so what).
Assholes in cars on phones are not the only killers on wheels, but they can be legislated against, identified and removed from the roads.