they released one in europe
i stand corrected. however, the rear battery door is likely different between usa models and europe, and the sgs2 screen size is 4.3" for at&t, but 4.5" for sprint and verizon for the sgs2. this likely means different sized battery doors, but i do not know for sure. unfortunately, it is a little more complicated.
my only concern is if the battery and battery door would fit correctly, and is made specifically for the at&t sgs2. if not, a definite gamble on YOUR part.
if you get the euro model, don't be suprised if it does not fit and you can't get a refund. and let's assume it does fit - what is the cost and international ups shipping? and if it arrives broken? no thanks for me - too complicated and risky.
see my post, above, of 2 companies, seidio and mungen, both reputable according to many other users here. yes, i wish samsung would offer an extended battery in the usa!
also, you need to ask yourself, why would samsung not want to sell it in the usa and make a profit in the usa? why? likely, because it is not compatible.