now that is something new and cool i didn't know until just now.
but back on subject, while i think metal cell phone cases are neat, i do wonder how much attenuation you are going to have of the signal trying to get through a material that is usually used to shield rf energy. so, yeah, those are cool, but do they render your cell phone inoperable once installed?
perhaps, just a metal carry case for a phone would be a better idea.