Why not just pay off the phone bill (the only honest way)...sooner or later they'll come looking for you after they've royally screwed with your credit rating?
You can always save up the necessary price of a new video card... the AIW Radeon will be obsolete in 6 months anyway, so you might as well save up for a bigger, better, faster card that you'll undoubtedly be drooling over then anyway.
There isn't any moral conflict here... you know what's the right thing to do.