Bunch of folks here need to read up on the topic of microwave-promoted chemistry. Google it. This has nothing at all to do with ionizing radiation, and nothing to do with local heating effects. It's much more subtle than that.
Summary: molecules have natural resonant modes. EM signals in the microwave band (which cell phone signals are) can and do cause various molecular vibration modes to be larger than they would otherwise. With the vibration modes amplified and tuned to some extent by HF EM fields vs plain thermal vibration, there are a LOT of variations in how chemical reactions proceed and the resulting reaction product balances. This is what the field of industrial microwave-promoted chemistry is about. Biologists haven't really caught up with this, because they are more interested in how things work _normally_. Anyone who thinks this effect could not possibly have any harmful influence on living organisms by shifting balances in the metabolic machinery, is just being stupid.
That's one definite potential for influence.
Another is that cells interact with each other by exchanging various messenger molecules and ions via ion-pump channels and pores in the cell membrane - which is an electrical insulator. Ionic potential between inside and outside of the cell plays a very important role in these - and you wouldn't be able to look at your screen and think about what you are reading if they weren't. Since that's how neurones fire. The complex of ways cells interact via ion channels is vast, and still being explored. (In brief, we still know squat.) Some of those inter-cell communications are related to cell division regulation, and contribute to cancer when they go wrong. So you think imposing HF E fields (no matter how small) across cell membranes can't possibly have any harmful effect? So then, go electrocute yourself. That's just a low frequency and higher current version of the same thing.
Here's another. Hopefully you'll enjoy this because it's so weird and unexpected. Think you know the structure and properties of the water molecule? Yes, but there's another form, semi-stable, to which microwaves can switch normal water molecules. I'm not convinced this is real, but it's interesting. Couple of starter links:
http://www.santilli-foundation.org/docs/Santilli-43.pdf http://benthamopen.com/contents/pdf/TOPCJ/TOPCJ-5-1.pdfPoint being, that if it _is_ real, that's another potential path for microwave influence of body tissue, because this form of water behaves quite different chemically.
I think a lot of people tend to be outraged by suggestions of cell phones being harmful, due to Confirmation Bias, in which they assume that since they use cell phones, cells phones must be perfectly safe. And to show otherwise would make them look like fools.
Problem is, there's accumulating evidence they are not safe. Another eg:
http://www.naturalnews.com/054165_cell_phone_radiation_brain_tumors_government_study.htmlMassive government study concludes cell phone radiation causes brain cancer
This is not a topic I save links on. I just decided when cell phones arrived that I'd avoid them as much as possible for philosophical reasons. Then later added Precautionary Principle. But really I don't care. The world is overpopulated and too many people are as unquestioning as sheep. By all means, carry your cell phones in your pockets.