There was an article on CNN
today about a new service. It's aimed at teen drivers and essentially turns off their phone any time they are moving at "car speeds". While I can see a lot of problems with the concept (what if they are a passenger, on a bus, etc....) it is an interesting idea.
The article talks about it being developed as a service from providers for something like $10-20/month but I bet you could build the same functionality into an android phone as an application.