40 minutes - 2 hours
The earpiece speaker in my wife's iPhone 4 suddenly stopped working. She could use the speakerphone, or a Bluetooth headset, but not the earpiece speaker. The iPhone 4 was already 2 years old, and out of warranty. I didn't want to pay for a brand new iPhone, and I didn't want to renew my cell contract.
The repair went smoothly. I followed iFixit's instructions, and everything went well. The printable screw guide really helped with the disassembly, and re-assembly. Once re-assembled, the iPhone powered-on during the first try, and everything worked perfectly.
Use iTunes to make a backup BEFORE starting the repair. Make sure you have a magnetic screwdriver, a pair of tweezers, and a spudger. I bought the iFixit Home Tech Toolkit, and it definitely helped. Go slow, and don't panic. The screws and ribbon cable connectors are really tiny! I also learned that battery replacement for the iPhone is a trivial job. If I need a new iPhone battery, I'll place another order with iFixit.