If you use mobile OR cordless phones for greater than 10 years you are up to 5 x more likely to get a brain tumor on the side of the head you use to talk more than 50% of the time. Bluetooth headsets are probably not going to help at all … if anything they may make things worse. I recommend speakerphone or car bluetooth.
 
Int J Oncol. 2009 Jul;35(1):5-17
Australas Phys Eng Sci Med. 2008 Dec;31(4):255-67