What would be interesting to know is if the international battery kit back fits the Korean GSII's since we know the Korean battery kit back does not fit the international GSII, and from what I've seen on the internet the AT&T version can not use the international kit (probably due to the back but the battery may still fit).
If anything I hope its just the back of the AT&T GSII that is incompatible with the international GSII cause if the battery and the back is different in size then I'll be really pissed cause that would mean that AT&T has a totally different size from all the rest of the GSII's which could make buying accessories really slim picking, one of the main reasons why I held out over the AT&T variant over the Sprint version was the similarities with the international version which means more accessories to choose from. So HOPEFULLY the Korean kit works.
Another option is to look at the batteries for the Indian version of the GSII since it supposedly has NFC as well but I have not seen anything on it. And of course we could just wait for AT&T and Samsung bring out the 2000mah battery kit for the AT&T GSII but I'd be surprised if they have any plans on doing that anytime soon if at all since Samsung will be busy with the Nexus and AT&T will be busy with their upcoming QHD and HD phones.
It's just a hunch but I went and ordered the Korean NFC 2000mah battery kit from exportprive for $35 USD (plus $20 USD "express" shipping) over the weekend along with a couple of those charger stands ($13 USD each) and I guess they will ship it soon so I'll be the guinea pig for testing the Korean battery kit and the AT&T GSII, wish me luck !