Personally I think this is a good idea. DriveAssist is software from Aegis Mobilty that will detect if a car is moving or not and if it does, the software then tells the cell network to hold the calls and text messages until the driver has stopped the car. Callers will be told that the driver appears to be driving the car at the time and have the option of leaving an emergency voice mail, which can then be put through immediately.
Given the, again in my opinion, good moves towards new state laws about using cell phones while driving, this is obviously a wave of the future. Although I understand the need to be specific with these various laws, there is a part of me that thinks the old reckless driving statutes cover this kind of thing just fine.