The Federal Communications Commission limits cell phone radio frequency energy emissions, called the specific absorption rate (SAR), at 1.6 watts per kilogram, as measured over one gram of tissue.

CNN: Scientists debate possible cell phone link to brain cancer

The Australian research focused on the thermal effects or specific absorption rate (SAR) of radio frequency radiation - a measure of its actual effects on brain tissue, whereas the earlier study simply looked at electromagnetic radiation levels.

BBC: Hands-free mobiles given safety boost