Got the iphone from a friend. No Wifi, no volume button and cracked back. From ifixit I learned to open the front and saw wifi antenna was disconnected. Decided to go whole hog. Ordered volume button and the back. Used a combination of the two guides to proceed.
Everything went well. I was super cautious until I had it all back together. Than got in a hurry to try it. All worked except ear sound. Opened it up again and found I forgot to re-attach the flex cable. After that it worked great. So now my wife has a nicer looking 3G than I do.
Slowly, slowly and check and check. I printed out the guides and marked up which screws went where. That made a difference.