Ah, finally, being a physicist has some use in real life :)
“Kroc, I love that chart! It has very little to do with the paper that is currently being hyped though. The radiation chart maps ionising radiation, but nobody is claiming that mobile phones are radio active. They are just saying the phone might be carcinogenic.”
To the best of my knowledge, the scientific consensus nowadays is that cancers are caused by mutating DNA, and we know two things which can make one's DNA structure change : ionizing radiation (electromagnetic waves bring sufficient energy to break the DNA's molecules) and chemical reactions (with tobacco, benzene and stuff like that).
Quantum physics tells us that unless non-linear optics come into play*, electromagnetic radiation can not cause ionization until you get light frequencies in the UV and beyond (X, gamma...). Sunlamps use UV to burn people's skin, that's why they may cause cancer.
Microwaves and radio waves have a lower frequency than infrared light, so they have a lower frequency than UV. Notice that if microwaves were dangerous, then visible light and the infrared light emitted by our own hot body should be dangerous too : we should probably avoid direct contact with ourselves.
In short, no physical phenomena known as of today may cause cellphones to cause cancer. Of course, the situation may change tomorrow, considering how limited our knowledge of cancer is. But as of today, the only statistical evidence of cell-phone induced increased cancer rates we know if is for people calling more than 45min every day : if you do not use your cell much, there is no reason to worry.
“I do use one It makes my parents a lot happier to know I have it with me when I take the bike to school. I do not worry about brain cancer a lot though, I rarely make any calls. It sits in my pocket or is used to send text messages.”
Actually, assuming that cellphone waves were dangerous, this is more dangerous than putting it next to your head :) As you mentioned, your brains are protected by a pretty strong barrier, the skull, but your testicles on the other hand...
*You'd need emission powers much stronger than any modern phone can emit for that, I think. At the lab scale we need very powerful lasers and hard to produce experimental conditions to see them. As the graphic above mentions, eating a banana would probably be more dangerous.