Q:

Can a faraday cage cell phone case protect wearer against possibly harmful signals?

I don't know much about harm a cell phone can cause if worn close to human body for prolonged periods of time, but I'd like to know if the phone's signals can be dissipated from the side of wearer's body by a small faraday cage.

A:

Yes, but there's a problem: that same radiation that may be harmful is what the phone needs to communicate with the network. You can't separate the two. So no harmful radiation = no communication.

A:

As Steven says - A Faraday cage will prevent the phone receiving signals.
There ARE practical ways to reduce the possibility that a phone will do you harm.
It is extremely uncertain whether cellphones do or do not cause harm and, if they do, how much harm they do cause. There have been a very large number of studies on the effects of non-ionizing radiation on the human body - both from cellphones and many other sources. Many  studies conclude that some harm may be caused and others conclude that no harm is detected. Even after poor studies, systematic errors and "confounding factors have been eliminated, the results are uncertain. This suggests that if there are effects then they are usually at a low level and easily buried in the "noise" or of a very variable nature and able to be affected by other factors and so become "hidden" from systematic analysis.
The most disturbing and perhaps most convincing studies related to certain types of brain cancer occurring in users who used cellphones a very very very large amount. Even these results are open to question and the number of people who use phones this was are small.
It seems likely that a few simple precautions should be enough to minimise possible harm, and in most cases it is likely that no harm or insignificant harm is cause by cellphone use. 

Minimise use - both length of calls and number of calls,
Carry the phone away from the head (as most people will do :-) ) and possibly somewhat away from the body.
Use a Bluetooth headset. This swaps one radiation source for another BUT Bluetooth operates at low power levels at all times.
Perhaps adopt a phone or use style that keeps the phone antenna as far from your head as reasonably possible.
I have not heard of this being done, but an external antenna located somewhat away from your body would greatly reduce the field experienced. 

