I was working under my Mini Monster, (Suzuki Sidekick on steroids), my iphone in my pocket, so I thought, had fallen out and on the ground where I put my foot and pushed across the ground. My foot slid easily across the ground atop my iphone, scratching the back panel and cracking it from one side to the other. It looked like crap, so I got on it and fixed the back panel and replaced the button assembly, which wasn't working properly, at the same time. I bought the Canadian Flag back plate, looks nice! The sad part is that my son was using my phone at his cousins and managed to crack the back glass again! So I'm ordering a new glass again and replacing it again...... The new back glass only lasted about two weeks! Arrrgh!
Repair took a couple of hours, as when your doing this kind of repair for the first time, you don't want to force anything for fear of breaking any part of the phone. The battery has some double sided tape holding it in place and that made me think I hadn't found all the release points, however after closely looking it over I figured out that it was only the tape.
The only thing I can say about the dismantling of the iphone 4 is that you need to follow the instructions and completely take it apart as per the instruction on ifixit. you can't cut any corners, you have to remove all the components or you can't make it work!