Here's a report that says 'maybe':

Electromagnetic radiation from your mobile phone may impair your ability to make snap decisions, such as when driving a car, an Australian study shows.

The study, which will be published in the journal Neuropsychologia found evidence of slowed reactions, on both simple reactions and more complex reactions, such as choosing a response when there is more than one alternative.

The researchers found these effects after people were exposed to electromagnetic radiation equivalent to spending 30 minutes on the phone.

...via Smart Mobs