Wirelessly posted (Mozilla/5.0 (iPhone; U; CPU iPhone OS 4_0_1 like Mac OS X; en-us) AppleWebKit/532.9 (KHTML, like Gecko) Version/4.0.5 Mobile/8A306 Safari/6531.22.7)
You can switch the bumper as long as you have the original packaging and a receipt, from what the Apple rep told me, when I had my first one. I ended up returning it though, because the first iP4 that I had wasn't very good.