Here is the diagram review of iPhone 3Gs logic board and mid chassis bezel assembly, from which you will see the full parts included into the iPhone 3Gs back cover. Meanwhile you will get to know where exactly each small part is located.
At the top ot the assembly, it includes iPhone 3Gs sim card tray, SIM card connector and 3Gs camera moudle. Between the main board and back cover, it is the 3Gs battery replacement. Along side the back cover, you will found the iPhone 3Gs chrome chassis bezel and all the side buttons.
Please kindly take note proffessional skill is required for the iPhone 3Gs main board and chassis assembly or disassembly, so please make it absolutely sure before your DIY. Considering those iPhone end users who are unafamiliar with iPhone repair, Aviso supplies the iPhone 3Gs full back cover assembly or touch screen half assembly with frame for your easy replacement. What you should do is to upplug the front screen assmembly, and transfer it to a new back cover full assembly. That's it.