So far, Google Wallet has only been open to people who have Sprint’s Samsung Nexus S 4G. This may or may not be because all the other carriers are teaming up to fight Google Wallet with their own NFC payment option, ISIS. But as Android always does, someone found a work around and then put it out to the world.
There is a fix over on XDA for the Google Wallet APK that allows it to work on the original Nexus S for AT&T or T-Mobile. The catch is it requires a full wipe of whatever ROM you are running but it has been confirmed to work with many different ROMs so far, including CyanogenMod 7. The best part is that you get the free $10 to start just like the official Wallet. Head on over if you are an intrepid soul.