story
Edit: I would also posit that in some cases, a short phone call can actually do a great deal to remove distraction if it is a settleable matter. The conversation you have in your head while driving may be just as bad as the one you'd have on the phone, except that it may dwell longer.
This is particularly true if you have a "lot on your plate".
Perhaps putting on an irritating radio station would help?
So in short: very few people can actually talk safely while driving, and the people that think they can probably can't.
1: http://www.npr.org/blogs/health/2013/01/24/170160105/if-you-...