I agree with Terbul. There is already a law that covers irresponsible operation of a vehicle. This law is unenforceable, and stupidly conceived. If you follow their rationale, they should be closing every drive thru window, because surely eating a Big Mac while you drive is at least as dangerous as talking on the phone. Also, I guess we're on the verge of outlawing screaming kids in the backseat.
The silliness of the law is exposed in the decisions it's forcing. A mounted GPS is ok. A handheld one will not be. Same for an MP3 player. It's just dumb.
If police see a vehicle operating unsafely they can already charge the driver. Passing a specific law for cell phones is a knee jerk reaction, and possibly some in the government think it's scoring them political points.