Girlfriends brother dropped his 3G and has the white screen now. No cracks in the glass. What part exactly needs replaced? Not quite sure, just the lcd digitizer?
If you are very lucky, it might just be the lcd screen connector popped off a bit. If not, it might be the LCD. I have changed these out - you need to know what you are doing though.
I just did the same thing, dropped it and had nothing but a white screen. Found directions and a replacement display at ifixit.com, not too difficult a job, just be very careful to not smudge the new screen when you install it.