Not a bad idea...but I see 1 problem.....what happens if a passenger wants to make a call? The phone is still going more than 10MPH, but the person isn't the one doing the driving....
Not to be a smart azz, but WHO CARES! We survived for a nearly a hundred years without being able to make calls while in a car, driving or not, and I don't see any pressing need for mere mortals to be "connected" 24/7 now. If they need to make a call, send a silly tweet, email, or text message, they can have the driver pull over.
Another good thing about disabling the phone when moving is that the rest of us also wouldn't have to put up with obnoxious loudmouths on trains, buses, and other public conveyances either. Like that loudmouth woman in the news recently who didn't shut the F up for hours on a train and was eventually hauled off by the cops after intimidating other passengers and the conductor when they complained (it was supposed to be a "quiet car", but we all know how rules are just for the other guys, right?).
If the only thing going on was essential communications that just couldn't wait, maybe this wouldn't be such a hot button issue for me. But the reality is that the vast majority of the calls, emails, tweets, text messages, and miscellaneous other crap is just that, crap. And none of it is worth your life, my life, or anyone else's life.
Jerry