There is a small independent research study that believes to have discovered a link between cell phones and cancer. The article is very interesting and I included the link below for your review. Considering there are 4.6 billion people using cell phones around the world*, the number of cancer cases associated with cell phone use is extremely small.
Nevertheless, if you are concerned about safety, you may want to consider using ear phones and keep your cell phone in a purse or holstered on a belt to keep the phone away from your body.
*Source: Heeks, Richard (2008). "ICT4D 2.0: The Next Phase of Applying ICT for International Development"