Incidence of the most common type of brain cancer in the U.S. has dropped 0.4 percent per year between 1987 and 2007. This would be about the very same period that we all started using cell phones. That doesn’t necessarily mean the drop wouldn’t have been steeper had we not used cell phones. And it doesn’t necessarily mean cell phones don’t have a long-term effect that we may see in years to come. It does mean that brain cancer incidence has plummeted just as cell phone use has taken off.
A cancer research blog goes into more detail. Bottom line:
It is understandable that people are concerned about mobile phones, especially because they are so widely used. But so far, the published studies do not show that mobile phones could increase the risk of cancer. This conclusion is backed up by the lack of a solid biological mechanism, and the fact that brain cancer rates are not going up significantly.
However, all of the studies so far have weaknesses, which make it impossible to entirely rule out a risk. Mobile phones are still a new technology and there is little evidence about effects of long-term use.