It sounds as though the jury is still out on whether or not cell phones can cause cancer. Concerns have been raised that RF energy from cellular telephones may pose a cancer risk to users. I thought that you might be interested in this article put out by the National Cancer institute. It really helps to explain some of the concerns and why research is still needed. You may also like to look at this article from the FDA which has a lot of information on the safety of cell (wireless) phones, how to reduce exposure, and the question of children using wireless phones:
Maybe these are good reasons to think about spending more time face to face rather than over the phone.