I replaced the screen on my 3gs after getting knocked off my bike and the iPhone coming off the worst from the whole experience, bought parts off eBay which included all the tools for taking it apart and removing the broken screen, took about 20 mins all in, one tip after I restarted my screen it was completely black and I thought it hadn't been successful, just do a hardware reset hold sleep and home button for 10 seconds and phone will light back up