Fulfilling but unsuccessful (and in the end, needless) surgery
20 - 40 minutes
After a heavy fall on its head my iPhone 4's ringer and vibrate ceased working. I had this repaired but the repair only lasted a month before the problem returned. I ordered what I thought would be the parts I needed would be from iFixit and had a go myself.
It was totally nerve racking as I didn't have much small electronics experience but the guides were clear - some sections could have had more / clearer photos. But I successfully replaced the vibrate motor and ringer switch. I should have replaced the headphone, ringer, volume control connector strip I think though because the problem wasn't solved when I put it all back together.
It took me about 3 hours to do. Lost a screw too. Get that magnetic mat! In the end I jailbroke the phone and installed a software ringer switch which turned on the audio so now I can hear the phone ring. But the vibrate motor is still not doing anything. Might have another go at some point.
Essential Electronics Toolkit
iPhone 4 (GSM/AT&T) Vibrate/Ring Switch
iPhone 4/4S Liberation Kit