How Does AT&T Detect Jailbreak Tethering?

If you thought Apple had it out for jailbreakers, get a load of AT&T: if they catch you tethering without an officially sanctioned tethering plan, you will now receive a nagging SMS message and accompanying e-mail. Not only that, but if you fail to respond to either of said messages, you will be automatically enrolled in the absurdly overpriced $45/month 4GB tethering plan (in addition to whatever data plan you already have).

As reported by AndroidPolice, the method for detecting unauthorized tethering is actually quite simple. It turns out that most jailbreak tethering apps, such as the commonly used MyWi app, work exactly the same as the built-in iOS tethering mode. That is, by routing traffic through an alternate, tether-specific APN (AT&T access point/router). Doing this allows AT&T to optimize performance and track usage. All they have to do then is look for alternate APN connections and test those devices for a tethering plan.

On the one hand, AT&T is in the legal right here: They offer a paid service and if you use it and don’t expect to pay for it, you’re stealing. Automatically signing you up for a tethering plan is pretty slimy, but legal nonetheless, according to your contract agreement.

On the other hand, it’s easy to see why jailbreak tethering is so tempting. $45 per month on top of your phone plan, data plan, and SMS plan starts to get pretty expensive, especially if you don’t use tethering regularly–perhaps only on the rare occasion that your home Wi-Fi service is out.

There are certainly those out there with grandfathered unlimited data plans tethering their laptops to their hearts’ content–these are the ones AT&T should be concerned with. But say you have a 2GB limited plan–it’ll still cost you an extra $45 to tether. It seems to me that those 2GB should be your data to use as you see fit, including tethering. Any data over your allotted plan amount, you still have to pay for (at a steep rate of $10/GB), so why not let those people tether for free? If anything, AT&T could potentially even make more money on limited plan data overages if they stopped charging for tethering. But I digress…

Some jailbreak apps, such as PDANet have already begun implementing tether-spoofing by routing tethering-mode through the standard 3G data APN. Until AT&T drastically lowers the price of tethering–like say, free for limited data plan users–I expect there to be a continued demand for jailbreak tethering. Let the cat-and-mouse game begin!

Think tethering should be free? Tell us in the comments!

Mike Keller is GeekTech’s resident iOS developer nerd. Catch Diary of a Developer every Tuesday here at PCWorld’s GeekTech blog.