The FCC there is no evidence and the FDA recommends people spend less time on wireless phones of any kind. http://transition.fcc.gov/oet/rfsafety/rf-faqs.html#Q11
HOW SAFE ARE MOBILE AND PORTABLE PHONES?
In recent years, publicity, speculation, and concern over claims of possible health effects due to RF emissions from hand-held wireless telephones prompted various research programs to investigate whether there is any risk to users of these devices There is no scientific evidence to date that proves that wireless phone usage can lead to cancer or a variety of other health effects, including headaches, dizziness or memory loss. However, studies are ongoing and key government agencies, such as the Food and Drug Administration (FDA) continue to monitor the results of the latest scientific research on these topics. Also, as noted above, the World Health Organization has established an ongoing program to monitor research in this area and make recommendations related to the safety of mobile phones.
The FDA, which has primary jurisdiction for investigating mobile phone safety, has stated that it cannot rule out the possibility of risk, but if such a risk exists, "it is probably small." Further, it has stated that, while there is no proof that cellular telephones can be harmful, concerned individuals can take various precautionary actions, including limiting conversations on hand-held cellular telephones and making greater use of telephones with hands-free kits where there is a greater separation distance between the user and the radiating antenna. The Web site for the FDA's Center for Devices and Radiological Health provides further information on mobile phone safety: FDA Radiation-Emitting Products Page.
And if you are geeky, or a ham radio operator, you know how to do the math on RF exposure using oet 65.http://www.fcc.gov/encyclopedia/oet-bulletins-line#65
I have an application that calculates power density at a particular distance or minimum safe distance based on exposure limits.
As everyone else has pointed out at one time or another, it's non-ionizing, but rf will definitely warm you up. There is a medical procedure called rf ablation that uses rf energy to heat tissue. It's used to treat chronic pain. They're not sure how it blocks the neurotransmitters but they think it "cooks" a protein that plays a role, iirc, but don't quote me on it.