I had dropped my phone cracking the screen. Still worked, just cracked. A friend gave me theirs which I dropped in a puddle, making the dock connector and home button not work, so I used the module from my phone. I then had a phone fully functional and one with a cracked screen and broken dock connector and (I would notice later after fixing) a torn ribbon connecting the camera.
Fixed the screen and dock connector and, with the exception of the camera I still have to fix, works great! Looks like new with the screen.
Keep aware of the camera ribbon when pulling out the logic board. Also, invest in a good case.
iPhone 3G and 3GS Mute Button
iPhone 3GS Front Panel Assembly
iPhone 3GS Dock Connector