A new Swedish study, via the Drudge Report, says that cellphones appear to raise the risk of brain tumors. People who appear to be at risk are those who have used cellphones for more than 2000 hours in their life, so the risk accumulates the longer that you use a cellphone. The researchers recommended hands-free use of cellphones to get them away from the head.
Cellphones use gigahertz radio frequencies that are also used in microwave ovens. Bluetooth wireless headsets also use gigahertz frequencies, so only wired headsets provide any protection.