It could be all kinds of things, Google won't (yet) tell. I'm annoyed about that myself (having bought a Samsung Galaxy 5 two weeks ago). Posted an item to the Google's Android Help forum, but no official response (yet...).
I'd be surprised, though, if it was the carrier. Too low camera resolution sounds more plausible (I suspect that's why I can't install Google Goggles, the Galaxy 5 camera does 2 MP only).
But... only the developer of the app could tell you which requirements they specified in the manifest.
A bit of background: an app developer can specify features her app requires. Like "device needs a camera". Or "device needs at least X x Y screen resolution". The market checks this list against the device you want to install it on, and... in your case, they don't match.