Just spent way too much time on the phone with AT&T. I haven’t completely resolved problems I was having with cellular access for my iPad, but I can give a warning: be 100% sure your email address is correct.
If it’s not, you won’t be able to log in again (since it’s your account name). And you won’t be able to retrieve a lost password, even with the web form that asks for IMEI and ICCID, because it’s sent to the wrong address. Nor can AT&T change it for you. And you won’t be able to stop automatic billing.
The whole idea of having plans that purport to be by the month, but expire, seems pretty lame, and is ultimately responsible for my problems. But that’s perhaps the topic of another post.