I have heard conflicting reports on whether it is possible to block the type of radiation emitted from cell phones, for example by consumer products/shields such as http://www.amazon.com/Phone-Anti-Radiation-Phones-inches-Black/dp/B006TGAQNA/ref=sr_1_1?ie=UTF8&qid=1439351881&sr=8-1&keywords=cell+phone+radiation+case.
Is it theoretically possible and what is the mechanism of such shielding?
Edit based on comments: I realize that it is not clear whether radiation from cell phones is harmful, I have seen studies suggesting that it is harmful but it is not clear that they do not have methodologic flaws, but regardless, that is not the question, the question is whether it is possible to block such radiation, what is the mechanism, and are consumer devices such as the one posted above plausible in their efficacy?