I'm not on AT&T, but I'm on Verizon, and Google Wallet works fine for me, including tap to pay.
There were apparently changes in Kit Kat and the latest Google Wallet app that allows the tap to pay functionality to work on carriers that were previously locked to Isis.
Well, I'm not sure if it works cause I haven't tried to pay for anything, but it does let me set it up and select Google wallet in the tap and pay section of the NFC setting.
I've used tap to pay a couple times, the phone does a little jingle and vibrates. It shows the status on the screen, and when it sees the authorization is successful it shows in your list of transactions.
Not all merchants will accept tap to pay, even if they have the terminals. Best Buy doesn't accept tap to pay.
I like the security that Google implements - for example, I paired my debit card, and my Amex card to my wallet. However, when you tap to pay, the payment method shows as a Mastercard.