AT&T is ruining a lot of people's days with a customer mailshot explaining that its "records show that you use [tethering] but are not subscribed to our tethering plan." iOS, of course, will disable the built-in tethering facility if you do not have an appropriate carrier plan.
There are a few jailbreak apps, the most popular of which is MyWi (previous TUAW coverage), that bypass the plan check and enable tethering independently. When you run MyWi or similar apps, your iPhone creates a wireless hotspot that allows you to connect other devices without the explicit permission of your carrier. Until now, people have assumed that AT&T either doesn't care or cannot determine that the traffic comes from a connected device rather than the iPhone itself. Clearly, those assumptions are incorrect.
OSXDaily.com has the full text of the letter. It goes on to state that users can either terminate their unauthorized tethering usage before March 27, or they will be automatically moved to AT&T's DataPro plan, which includes tethering and costs an extra $20 per month. DataPro is also capped at 4 GB, so presumably any customer on the grandfathered unlimited data plans from older iPhone plans would also lose that facility.
AT&T aggressively moving against unauthorized tethering originally appeared on TUAW on Fri, 18 Mar 2011 08:35:00 EST. Please see our terms for use of feeds.