Still people are clueless as how AT&T is able to easily identify unauthorized tetherers resulting in warning notices for customers but here Android Police has provided some insight into how AT&T is able to identify users who are using the unofficial tethering option.
Jailbroken iPhones typically use the same tethering technique as a standard iPhone, the one that’s already present in iOS. This method exposes tethering activity quite readily, because the iPhone, when in tethering mode, sends traffic through an alternate APN (AT&T access point/router) for the express purpose of identifying the traffic as tethered data. This makes it extremely easy for AT&T to identify whether or not an iOS device is utilizing tethering, and just how much of their data is consumed via tethering.
Some tethering applications for iOS make use of alternative methods and route tethered traffic through the phone’s normal data APN, but by and large, most jailbreakers stick with the stock application because it’s easy to use and doesn’t require any complicated setup. In fact, many iPhone users jailbreak for the sole purpose of avoiding AT&T’s tethering fees (for why, see next section). These are the people AT&T’s is going after.
Not long ago, JuneFabrics released an update to their PdaNet tethering app for iPhone which claims to be able to hide your tethering usage from carriers. I hope many developers are working hard to release updated version of their jailbreak apps to stay ahead of the cat and mouse game with AT&T.
[ via iclarified ]