I keep mine switch off ..if i need to use it I just pull over in a safe position switch off the engine and remove the keys..
Another point is why cant they now make all new phones so they are unable to get a signal inthe car..
Firstly it'd probably be easier to make put shielding in cars to stop the signals rather than stopping it at the phone.
Secondly, there are problems with that. What if you roll your car and are trapped but can't call for help because the phone doesn't work in the car?
It's better to just increase policing of it and make example of those who they catch, sorry to those on here who would be caught but seriously it's not good for your overall health.
On a side note, they should also ban smoking while driving because it a) looks trashy, and b) can be distracting - lighting up, smoking, emphysema coughing, putting it out, flicking ashes off... all that jazz.