That would be a pretty cool idea. The only thing that Moj.io has over what you're proposing is the ability to be always-on, even when a phone is not in the car

That would be a pretty cool idea. The only thing that Moj.io has over what you're proposing is the ability to be always-on, even when a phone is not in the car (hence the touted ability to detect hit & runs and towing). It would be interesting to maybe have a system that uses and assists apps on the phone but can switch over to its own connection when in a parked car.