Most frustatingly I have smashed the screen of my iPhone 4. Any advice on whether any of the cheaper non-Apple replacements are any good? (A friend spent ?160 replacing her screen a few months ago...ouch!).
For the 3GS you could either buy just the screen or for more money the screen with some electronic attached. I went with the latter since I'd didn't want to play around with a hairdryer to melt the glue. I don't know if it is the same for the 4.
The replacement parts can be found on Amazon or eBay.