I used to clean te inside of all my friends cell phone screens by taking a razor and carefully prying up at the corner of the top screen. you should do this in a room with little dust. Then find a super soft clean rag (like the nintendo screen cleaning ones) and gently clean out all of the crap stuck in there. After this is done, the glue should still be sticky and adhere the cover back to the screen. If not, razor up a few very thin pieces of scotch tape and cover the crack entirely, this will also help prevent future dust from getting back on the screen.
Make sure you check and see if the warrenty is still good first, and i wouldn't try this unless your warranty isn't any good, (or if you really really want your screen clean.
I have done this procedure to my Motorola RAZR about 5 times now over the course of a year and a half...still works good too.