AT&T will begin revoking unlimited data plans from customers who jailbreak their iPhones to use unauthorized tethering services, the company confirmed to Boy Genius Report today. AT&T's action applies to all customers tethering on the sly, whose monthly bills will automatically have AT&T's 4GB tethering-approved plan added to them if they continue to tether past a certain date.

AT&T notes that earlier in the year, it began contacting customers who were tethering without an approved tethering plan via letters, e-mails, and text messages. These customers, including those with grandfathered-in unlimited plans, have two choices: stop tethering, or switch to a tethered plan. If the customers kept tethering but didn't switch their plans, AT&T said, the plans would be switched for them.

For those who pay $30 per month for unlimited data, the minimum tethering plan (2GB of smartphone data and 2GB of tethering data) would be an increase of $15 per month. Those customers would also never be able to switch back to unlimited data, as that plan no longer exists.

Customers engaging in illicit tethering may get their plans bumped as soon as August 11, according to 9to5 Mac, regardless of the fact that when unlimited plans were still an option, there were no stated restrictions data use. The notifications AT&T has been sending to its customers each include a date that their tethering will no longer be tolerated, and they will have to choose between an unlimited plan without tethering, or a tethering plan with limits.