Add a bit of personal experience here. Google gave its employees unlocked Android phones (not once but twice :-) and some of us (like me), put our AT&T sim card into them and used them instead of our plan phone. There was a 'feature phone' data plan that was $15 unlimited and there was the $10/month 'tax' if you had an iPhone.<p>Using the cheaper unlimited plan worked for a long time, and then AT&T started 'automatically' switching people to the smartphone tax if their IMEI indicated they had an android phone. I did what any reasonable person would do, cancelled my AT&T contract and signed up with t-mobile :-)
Lots of discussion of this elsewhere. It looks like some people who don't tether (but use a lot of bandwidth) are also getting the message, leading people to believe to that AT&T is looking solely at bandwidth usage.<p><a href="http://modmyi.com/forums/iphone-news/755094-t-cracking-down-mywi-tethering.html" rel="nofollow">http://modmyi.com/forums/iphone-news/755094-t-cracking-down-...</a><p>I use TetherMe ($2 in the cydia store, instead of $10 for mywi, enables native tethering), and I haven't gotten this message.
These e-mails from AT&T are almost always smoke and mirrors. I'm on the same data plan I had in the Cingular days and have received dozens of e-mails and texts warning me that I "may be violating my contract" and that they're going to switch me to the $60/mo plan.<p>I've yet to be switched away from my $10/mo data plan.
Was posted earlier today with a large set of comments: <a href="http://news.ycombinator.com/item?id=2340275" rel="nofollow">http://news.ycombinator.com/item?id=2340275</a>
It's unlikely AT&T is doing anything fancy at this point, but there's potentially much more to detection than TTL. NAT devices make an attempt to be transparent at layer 4 and try not to interfere with it. Host OS fingerprinting can rely on a combination of options at that layer as well including but not limited to windowing scaling MSS. If AT&T cared to go the distance, it would be very difficult to get around detection without interfering with the TCP/IP stack.
There is a greater underlying issue here which seems to be missed.<p>I have paid £x to use O2's (or in this case AT&T's) network, not only that but I also had to partially pay for the handset.<p>O2 should not really give a damn about what device I use to access their network - sure, they may have sold me a handset with an Internet plan, but it is MY DECISION to use whatever device I see fit to use that network.<p>If I am allowed to use whatever device I want but it was capped to say 4GB, I would have no issue, but as it stands, I am not only paying to use the phone, but an additional bullshit cost to tether the phone which technically should be none of their concern.
I'm curious to find out what you guys / gals think about this. Is this just a fear tactic? Or, does ATT have a legit way to check if you're doing unauthorized tethering. Any of you get hit with this text on accident (false positive)?<p>EDIT
Removed the '(Ars)' from the title. N00b mistake :)
Unless they're performing a deep packet inspection, there's no good way to tell if you're tethering. Usually tethering option uses user name that differs from non-tethered option during authentication. If your unathorized tethering application sits on the device, it simply shares non-tethered connection, hence the user name doesn't change. The only plausible explanation w/o going deep into packets - bandwidth or some unusual ports usage.
They can detect this only by listening traffic. Isn't this require some court order for wiretapping? =)<p>Also, what's about if I setup permanent openvpn connection from the phone to some dedicated server?