From the NHTSA site:
Research shows that driving while using a cell phone can pose a serious cognitive distraction and degrade driver performance. The data are insufficient to quantify crashes caused by cell phone use specifically, but NHTSA estimates that driver distraction from all sources contributes to 25 percent of all police-reported traffic crashes.
What sunk it for me was actually reading the study that showed that cell phone usage was worse than drunk driving.
Go read it, its interesting stuff to dig into the details of the USA Today headlines.
What the study showed was that:
a) people who know their driving is being monitored while on a driving test machine may drive better than they do in real life. Unless you've usually got a dude sitting next to you in the car with a clipboard staring you down and actively critiquing your driving.
b) from that ideal, driving with a cell phone is minutely worse in terms of reaction time, but nothing that would translate into a "success/fail" situation...they were looking at stuff like "oh, in a perfect world its 10 seconds, with a cell phone, it was 10.3 seconds". I'm betting in the real world "holy cow, look at that hot chick/hmm...I guess I better file my taxes" world, its 10.3 seconds and 10.3 seconds.
c) the drunk driving (.08 ) numbers were slightly better than the cell phone numbers.
What it "proved" to me was that neither driving while .08 or with a cell phone was a significant distraction and that I'd like to see some sort of real world testing where they hook people up to the tester for 3-4 hours and measure their responses to very occasional input towards the end, vs the .08 and cell phone reaction times.
If THAT didnt sink it for me, it was over when the CHP did a study on behalf of the CA legislature who wanted to pass anti cell phone laws and came back with a conclusion that cell phones were not a contributing factor to accidents in CA. They were then directed by the legislature to consider any accident in which a cell phone was present (in use or not) to be an accident caused by a cell phone. With that revision, they came back with a low double digit number and some new laws got passed.
Funny how you start with a conclusion and end up with some 'facts', eh?