I'll try to put this one to bed here. There are three ways that radiation can interact with the body, that depend on the frequency. One concerns low frequency radiation and is irrelevant here, as mobiles use far higher frequencies.
The one people are worried about is ionising radiation, which is the one that can cause cancer. It can happen, if I recall, when the photon of radiation impacts the nucleus of a cell and ionises an atom in a DNA strand. If enough photons do this to enough atoms, it can cause the cell to become cancerous. But it takes a very high dose of EM radiation to impact enough atoms to do any damage. And here's the good part - It is also totally irrelevant here. EM radiation only becomes ionising above a certain energy threshold, and the energy of a photon is proportional to its frequency. The frequency of radiation used by mobiles is FAR too low. We're talking a million times too low here. Mobile radiation is not ionising.
Which means the only relevant effect is thermal - The amount by which the brain can be heated by the phone. The desire comes in at a maximum of 1.48 watts per kilogram. Apparently the average human brain is 1.3-1.4kg, so we'll go with 1.35kg for the sake of argument. Therefore, at MAXIMUM levels, your brain absorbs about 2 watts of energy.
The brain is composed mostly of water, so we'll assume a specific heat capacity of about 4 joules per gram per kelvin, a little less than that of H2O. What that means is that it takes 4 joules of energy to raise the temperature of 1 gram of brain matter by one degree Kelvin (The same as one degree Celsius).
The brain weighs about 1350 grams, so to raise the temperature of the brain by one degree you need somewhere in the region of 5400 joules. And at 2 watts of input from the phone, that means at most the phone would increase the temperature in your brain by one degree in a 45 minute phonecall. But that's assuming that the phone constantly operates at its maximum power, which it wouldn't, not to mention the fact that the brain can easily cool itself to compensate for that. The phone has no effect.
PS. I know it ignores a lot of the biological factors, but add to that that every reputable study ever done has found no evidence whatsoever of any damage by mobile phone radiation, and you can rest assured that you're safe. The studies that DO find things are almost always by people who set out to prove it is true. So they find a way to make it true. Look, this rat developed cancer when exposed to mobile phone radiation On a level 2,000 times greater than is used in a normal phone on a creature a tiny fraction of your body mass! Take everything you read on this matter with a good tablespoon full of salt.
