If you're annoyed with your iPhone slipping out of your hands, here's an idea: replace the glass back with skateboard grip tape. Sure it might char up your hands but it'll never ever slip again!
Jokes and scratchiness aside, I think it actually looks pretty awesome. It's clean but still full of character. The guy who made this actually made the grip tape iPhone out of necessity, as he dropped his iPhone, breaking its back. He tried other materials first (silicone, sandpaper, etc) but eventually settled on grip tape.
If you dig the look, you can buy a laser cut, grip tape sticker (made by the same guy) for only 5 bucks here.