Hey Guys,
I did a change for my niece who smashed the front digitizer and the back glass.
I did the whole thing myself. It was fiddly, but not too difficult. Few tools needed.
A couple of hours (with some coffee in between) and hey presto.
If your iPhone 4 is broken front or back or both, and if your eyes are good, then why not dive right in. There is a great reward in disassembling the whole iPhone and rebuilding it and then everything works great!
Have fun.
PS you can grab your parts here: http://www.ifixit.com/iPhone-Parts/iPhone-4-Display-Assembly-GSM-ATT/IF182-003