Three of Japan’s cell phone companies have concluded that cell phone radiation doesnt cause genetic damage to cells. Granted, the study was conducted by cell phone companies, and they have a stake in the findings…however, some results have been published by the World Health Organization (WHO). WHO has recommended that there be further studies, in light of other studies. There was a highly publicized study by the Dutch TNO a few years ago stating that they had found prolonged exposure to cell phone radiation to result in dizziness and headaches in humans. (PDF here)
NTT press release is here.

WHO report can be found here. with more info by the WHO on EMF here.

for a good intro - have a look at the “How Stuff Works” site.