A new study published by Tel Aviv University suggests that prolonged cellphone use, especially while next to the users head, has been linked with salivary gland and brain tumors. There have been reports of this nature before, but because of the dormant tendancy of brain cancers, the results of studies were often hard to track.
The researchers suggest always using your hands-free device or at least limiting the number and length of calls. It also suggests that people in rural areas, where reception is low are particularly at risk due to the amount of radiation emitted by the phone to maintain reception.

Here’s another site with the top ten emitters of radiation in the US phone market.