This is a bit on the scary side. Of course they know our data usage, but imagine getting that email from AT&T saying that their records show you are tethering, "but are not subscribed to our tethering plan."
Whoa. As website TUAW points out, most just figured AT&T didn't know when iPhone owners were tethering their device. Well that's not the case. They know. Heck they probably know you've been when you've been looking at those nudie pictures, too.
So what are they doing about it? They are sending out one of those friendly, yet authoritative, emails reminding you that you are using this extra data and not on their plan. You can do one of two things: 1) stop tethering 2) don't stop tethering and automatically be transferred (after March 27th) to their DataPro plan for an extra 20 bucks a month. Choices choices.
Well, those using jailbreak apps like MyWi will have to do one of the two, at least that's what it looks like for now. It's unfortunate that they won't allow the tethering. Heck, you still have to abide by the 2GB a month bandwidth cap or pay them by the GB.
Any readers out there get a similar email? We'd like to know what those who got the email plan to do once this restriction is enforced. Let us know in the comments if you'd like. OSX Daily has the full text of the email on their site.