I did a repair recently on an Apple iPhone 3GS. Parts were cheap for the backing and the power button. All under $10 including shipping. The repair was to replace the back of the phone as well as replace the power button due to a drop that occurred. No small feat but it’s pretty annoying if you are missing a power button especially if you need to put your iPhone into DFU mode or simply put it back to sleep.
What a lot of the videos out there don’t tell you is that there is adhesive on some of the parts like the antenna assembly and battery for sure. The top glass section doesn’t get worked on in this fix, however it too has a slight adhesive bond and weather stripping I call it around it that can get damaged on the botton when using the plastic tool to lift it. Alternatively you can use a suction cup. I included some of the pics here for reference.
The take apart can go quickly but make sure you record which screw goes where since they are different sizes and it gets confusing later when you have to put it all back. The button assembly is the hardest to put back. Screws here are angled and very tiny! I advise you to use a magnetic screwdriver and take photos of the tear down stages. I strongly advise also when you put back the volume button that you keep the pads on it, they will fall off, put them back the best you can because it allows for the button to fully rock back n forth in a smooth way. The back doesn’t come with the speaker screens which essentially are just metal mesh stickers. They pop out easily and keep their stickiness. Lastly, I don’t know for sure but I did fry a 3G once when the order of the flex cables got put back wrong. I would stress that it is very important to slowly make sure you put back each flex cable in the order they go. Obviously this means take apart starts with 1, and reassembling starts with the highest number. On this phone that was #7.
I probably spent 4 hours doing the whole job with a 45 min break to overcome frustration. If I had to do over again and being familiar with the processes now, it would probably be half of that.