The problem lies, in part, with what I guess you could call the aesthetic of multitasking. We love to think that we're good at it, but -- as research has proven
over and
over [warning: first link is a pdf download] -- we are actually really shitty at it. The same is true of driving. I remember as a kid riding in my dad's car, how he would try to change the channel on the radio, or do something with the A/C, and
immediately start veering the car off the road. At stoplights, the minute he stopped thinking about it, his foot came off the brake and the car would roll out into the intersection.
I don't think fixing cars or cell phones is going to get to the root of the problem. The root is that people think they can do more than one thing at a time and not trip over their own damn feet. Since changing the culture seems out of the question, no amount of technological fixes is going to save us from trying to do more than we're cognitively equipped to do.