There was a very good article in Popular Science a while back, here's the online version:
http://www.popsci.com/science/article/2010-02/disconnectedNow, I'm not sure how closely it matches the physical article (which I own), but it looks pretty much intact. Apart from reading the article yourselves (which I recommend), here's a notable aspect from research noted in the article:
Gene Expression
Research by Igor Belyaev, an associate professor in the Department of Genetics, Microbiology and Toxicology at Stockholm University, has shown that EMFs can affect gene expression -- the mechanism by which genes are activated and "speak out" -- in human and animal cells. Belyaev exposed human lymphocytes, a type of white blood cell involved in the body's immune response, to EMFs at 915 megahertz, a common cellphone frequency. The samples were taken from healthy people and those reporting EHS symptoms. In cells from both types of subjects, Belyaev observed a stress response that altered gene expression. The stress response induced by EMFs at 915 megahertz disrupted the body's DNA-repair machinery, he concluded, thus making it harder to fix the kind of cellular damage that can lead to cancer. In other research, Belyaev has found that cellphone-frequency EMFs inhibit DNA repair in stem cells; DNA breaks in stem cells are critical to the onset of leukemia and some tumors, including gliomas.
Stress response does indeed cause changes in gene expression; however, says Repacholi, "lots of experiments can find effects, but that doesn't translate into the whole organism, because the whole organism compensates. The gap between a biological effect and an adverse health effect is a big one."
There are five pages in the online article, this was from page #4. Conclusion? It may be reasonable to assume that, while cellular devices do not cause cancer, electromagnetic frequencies interfering with the repair/replication of DNA might be possible as factors which can lead to cancer over a sustained period of time.