Kreg, I bought the one from M.A.D., it was called their Super Crystal call. I sure hated to scratch up that great looking smooth glass surface but that's what you have to do!! And I mean scratch it up really good!! They usually supply you with a piece of very ruff sand paper, use this to scratch it up first. Then go to a finer grain apaper next. Go every which way, not in just one dircetion!! Like Richie suggested, get yourself a glass call surface conditioning tool and carry it in yourr vest with you.
After you get this job done, I have found that a Purple Heart stiker sounds just super with this kind of call!! This is one of my favorites, bar none!! Good luck!! <img src=icon_smile_big.gif border=0 align=middle>