And I'd think most of those ideas suffer various problems too. Most ideas trying to solve social problems end up over-engineered and even more so when trying to iron out the problems.
There are plenty of people with mobile handsets which number other than 1.
Those with 0 for example, either through battery being dead, stolen, lost, quick run to the shops without picking up a phone or simply choose not to have a phone. We seem to now be blocking them from using the car. Well I guess we'll need to engineer some sort of override to allow for that? Now the system without the override is a worse experience for most people, but being the same law abiding, socially caring people who wouldn't text whist driving anyway, they won't use the override except in a genuine situation right?
More than 1, well I guess that only one is blocked so no problem texting etc. as we go. I guess we could implement the cell site thing to ensure all the phones in the car connect to that right? Well what about passengers in the car etc. Guess we need some vision systems so the car can also see who is operating the car and the phones?
And whatever you do you can bet those who are willing to break the law still will, they'll find a way of getting around it. So you still need to find ways of actually enforcing the law anyway...