cnn.cn, an OEM cellphone parts company from Hong Kong. There are similar flat metal backs that can be found on eBay, but this is one of the few places that sells it with a beveled back. The slight bevel rounds out the back of the phone, making it feel less sharp. It also adds a tough industrial look. For even more durability, adding a bumper and a front screen protector protects your phone further while still managing to keep the iPhone's refined look. The best part is, it's simple (only requires removing a couple screws; see ifixit's tutorial for installing an iPhone 4 rear panel) and cheap ($12.99 for the metal panel).
1. Remove two screws at the bottom of the phone with a Philips #00 screwdriver.
2. Slide back panel off by pushing the panel up with your thumbs. 3. Line up metal panel and slide down. Return screws.