Yes, phones give off radiation, which sounds scary. But this is not radiation in the sense of Chernobyl or Fukushima with radioactive decay of nuclear material. Phones emit electromagnetic radiation, i.e. light, in frequencies corresponding to microwaves. Not that microwaves are automatically safe for humans, but again it needs to be put in perspective.
Point #1 - Energy. Some forms of electromagnetic radiation (X-rays and gamma rays) correspond to photons with a lot of energy, and if they hit your cells they can break apart DNA molecules leading directly to cancerous mutations. Microwave photons have energies less than that of visible light, and do not have enough energy to disrupt molecules. They can only make molecules wiggle, i.e. heat up. This is what we use them for in microwave ovens.
Point #2 - Intensity. Totally separate from the energy of individual photons is the total intensity of the radiation, i.e. how many of those photons are beamed into your head. Obviously, putting your head in a microwave oven wouldn't be good. But the intensity of radiation from the cell phone is tiny compared to an oven. You can't boil your blood with a cell phone, and no you can't even pop popcorn with cell phones. I have seen that cell phone use may cause local temperature increases in the brain, but wikipedia notes that "the level of temperature increase is an order of magnitude less than that obtained during the exposure of the head to direct sunlight." This suggests to me that an indirect carcinogenic effect caused by the temperature increase in the brain would be smaller than that caused by wearing a hat.
'OK, Poindexter', one might say. 'This theory of yours is all well and good, but what about the actual data. WHO wouldn't scare us to death over nothing.'
Here, I'll defer to someone who knows something about this sort of thing (thanks to the Bad Astronomer for the link). There are a couple things in particular I'd point out:
If cell phones do cause brain cancer, then surely epidemiological studies over the past few decades would show an increasing trend, but "studies in the US, New Zealand, Denmark, Norway, Sweden and Finland have found no such trends. In the UK, the incidence of brain cancer has been flat for the past few decades."
This graph ties together a number of studies on the subject of cell phones and cancer. The horizontal line represents what you'd expect if cell phones neither caused nor protected against cancer. The pooled estimate combining them all is smack dab on the no effect line.
And finally, just what did WHO actually say? Apparently, there are several different possible classifications. Cell phone radiation was placed in category 2B.
Group 1 is the highest, reserved for things like smoking, asbestos, alcohol and so on. It means that there’s extremely strong evidence that the thing in question causes cancer.
Group 2A includes things that are “probably carcinogenic to humans”. Here, the evidence is “limited” in humans, but “sufficient” from animal studies.
Group 2B – this is the one that mobile phones now fall under – means something is “possibly carcinogenic to humans”. It means there is “limited evidence” that something causes cancer in people, and even the evidence from animal studies is “less than sufficient”. Group 2B means that there is some evidence for a risk but it’s not that convincing. This group ends up being a bit of a catch-all category, and includes everything from carpentry to chloroform.
Quoting WHO's definition of limited evidence: 'Limited evidence of carcinogenicity': A positive association has been observed between exposure to the agent and cancer for which a causal interpretation is considered by the Working Group to be credible, but chance, bias, or confounding could not be rules out with reasonable confidence.
So whatever positive correlation WHO sees is not distinguishable from random chance at a statistical level of signficance.
All the screaming on the media is about a tiny effect that may not even be there, and which has no possible theoretical basis.
But maybe it is there! Maybe it is. All scientific knowledge is tentative. As the expert notes, other studies are already underway, so it's not as though scientists are uninterested in learning more. But the alarmism I've seen is really unjustified, considering the actual state of knowledge.