From elsewhere on the web:
"Ok guys, I hate to break the bad news to you, but I think have fixed many phones in my day and unfortunately that "glass lens" is meant for sale to manufacturers (like Samsung or whomever else makes the razr m's screen). The front "lens", or the digitizer touch display as its actually called, is fused together with both the led display and aluminum bezel in the factory. If you try to take them apart you'll find a certain clear oily liquid in between the digitizer glass and led display, kind of like mineral oil. You'll never be able to put the two together properly but moreover, it's very unlikely that you'll be able to get the old cracked digitizer and led display without doing further damage. Sorry but if you follow the link and order, you'll be wasting $20. Just thought I'd give you a friendly warning."
A replacement digitizer runs for 200 to 300 dollars, so a eBay replacement of the phone in its entirety seems to be the best solution so far, all things considered.