The National Safety Council is all over the press calling for an immediate ban on the use of cellphones while driving. News media reports typically quote a representative of the NSC claiming that cellphones have been shown to be distracting. Thats not enough in my opinion. I frequently use my phone while driving as do 100 million Americas per the NSC's own data, and I do not think it's risky behavior. I could be convinced otherwise only if there was a showing that a cellphone ban will cause a substantial reduction in the number of accidents. This "fact sheet" is a bit more substantive than what is being quoted in the press, but it still doesn't provide a satisfactory answer to this question, mostly because it fails to actually cite the studies it makes reference to, and so its impossible to tell whether or not these results are being spun. The only study that is referenced is a study on texting while driving which is substantially different. They do cite this statistic:

Cell phone use contributes to an estimated 6 percent of all crashes, which equates to 636,000 crashes, 330,000 injuries, 12,000 serious injuries and 2,600 deaths each year. (Harvard Center of Risk Analysis).

Thats a start, but wait, what does "which equates to" mean? It sounds like they are assuming that all crashes are equal, and 6% of crashes result in 2,600 deaths, and so cellphone use is implicated in 2,600 annual deaths. But you can't just extrapolate like that. Are cellphone related accidents more or less likely to be fatal than other kinds of accidents? What does "estimated" mean? Are these real numbers or not? What about "contributes to?" What percentage of these are cases where the driver was drunk and on the cellphone, or speeding and on the cellphone?

Unfortunately, I can't tell, because no actual study is referenced. When I google around for the Harvard Center for Risk Analysis (SIC) I get studies that have very much the opposite conclusion:

Study Finds That Restricting Cell Phones While Driving May Be Premature, That Benefits May Be More Compelling Than The Risks

Are they citing a newer study? What study?

Many of the other claims made in this fact sheet are also questionable or involve studies that reach conclusions which have been contested by other studies which aren't mentioned here.

The fact is that you have a ban in California. Has there been a decrease in the number of automotive fatalities since in the ban was put in place? This is a very simple piece of data to collect. The fact that these people aren't trumpeting it leads me to suspect that it doesn't reveal what they want it to reveal.

Cell Phone Use While Driving Fact Sheet