Comment by peterbecich

This would never be implemented I realize but here is a possible solution:

New law: driver's phone must be in semi-disabled mode

The phone can already infer it is inside moving vehicle. The bigger challenge is, how to determine the phone belongs to the driver?

Say N passengers in car (including driver), each with cell phone.

When phone infers moving vehicle, it attempts to mesh with other phones in the vehicle.

If N=1, driver is solo, phone semi-disables

If N>1, phones ask users to vote on who is the driver.

Result: 1 phone disabled (Voting tie disables both/all)

The only inconvenience here is to a passenger with a phone-less driver.