I spent quite a bit of time trying to figure out how they do it. Then I followed the Corporate trail as to who's software or services they would be using to do this... and lo and behold - I found the answer. The have picked up Ciscos Openet - Orange France - and using FusionWorks DPI to detect tethering. I don't know exactly how this works - so if you get this post - there is your answer. How do you conceal tethering through Deep Packet Inspection? And is this even legal for AT&T to do because of some of the Privacy acts from 1988 to now. The worst part of this is that after talking with AT&T - I have the $30.00 unlimited data plan grandfathered into my contract. I have had the same plan for 3 years now - and AT&T claims through their contract they can just add changes and I must adhere to them. Not as if I signed a contract stating I agree with the new tethering policies. I didn't. They just enforce. And you can't just cancel the contract without paying the termination fee. They waited til after I renewed to hit me with the email and texts. Dirty in my book! The kicker is I don't use that much data at all. I rarely tether and only do so when there is no access around and I must service a client - Then I usually use it for LogMeIn or email. My kids use the iPhone for Netflix and they use a ton of data. As pissed as I was with AT&T - I let them know if they are trying to cut down on usage - I wasn't going to comply.... I was going to run the crap out of Netflix and quadriple my usage - just to prove a point - I can be an ass too. They didn't like my statement to much! So - anyone who can figure out how to hide tethering through DPI is going to be a hero.