Wow, that's weird! I just ordered their AT&T service here in GA a week ago online and no issues. I just went back on the site and did the same as you guys and sure enough, after I entered my zip code, I'm only prompted with a pic to order a TMobile SIM. Funny tho in the fine print at the bottom it mentions stuff about AT&T and TMobile???
I'm glad I got mine as TMobile prepaid sucked for me so I had to change to ST AT&T and been very happy with their service and data connection.
Although, I just went on Walmart.com and see you can still buy AT&T SIMs for $14.95 or an AT&T SIM/plan for $54.95, so looks like you can see get it from Walmart.
I wonder why they pulled AT&T SIMs/plans on their website??????