I recently upgraded my brother to a different brand of phone. He had my older iPhone 4. Swapped the 4 for my dads beat up 3GS. I had used the four so much (college, band touring) that the battery was almost flat. So was the home button. You had to gouge at it to work. Being a former Apple employee, plus a technician outside of that, I knew I could get him up and running after spending a few bucks. ;]
This is the funny part. I ordered the parts from Amazon to begin with. Since I didn't think my dad would have the 4 for too much longer. I tore everything down to realize that the Amazon seller had sent me the sleep/wake button. I wasn't paying attention when I got the part. So, since iFixit is a trusted service, I ordered the parts from these guys and everything was perfect. Fresh home button, awesome battery life again (with a juice pack pro too.) :D
It's all about the tools you have to work with. Get a toolset from these guys. The ones they send in kits from other sites are not very effective.
Also, do yourself a favor and have an organizing tray for all the little screws!