IIRC, though, the company that put these out ended up recalling them for shorts or something. I personally would not buy one of these, aftermarket mods like this scare the hell out of me.
I'd stay away from these types of mods, it'll drain you battery quick (as if it doesn't drain fast enough already!) and it may turn your iPhone 4/4S into a ticking bomb! (j/k on that one)...