This won't work- as long as it is up to the individual, it won't work because human nature always says, "this won't happen to me, I can handle it". The only solution is a forced solution, a built in 'feature' that will detect the speed at which the phone is moving- above, say 25 mph, it disables broadband only- WIFI and BT would still work. This obviously would involve GPS but should be separate from the GPS option that can be turned off by the user. I think that is very doable, the problem is, many people would not by such a phone, but if it is federally mandated, they'd have no choice.
I personally do not think we should legislate anything to protect the individuals from themselves ( frankly, if you don't care about your own life, go ahead, knock yourself out), but in this case, more often than not, the individual is endangering everyone around them!
Nissan were early on the scene with electric cars but are failing to stay ahead. I wish they'd concentrate on producing an attractive model with better range rather than gimmicks like this. The Leaf is not great in performance terms compared with a Tesla and the Japanese in general struggle to make cars look attractive to European buyers. Having limits placed on their phones is going to put customers off. It would have to be a legal requirement across all vehicles and that's unlikely to happen.