How do we suspect AT&T are able to determine when a device is being used to tether?
"I helped my boss through this one... I had him call AT&T and explain that he received a message about something called "tethering" and to act dumb and explain that he is a heavy pandora and Netflix user and doesn't understand why he's going to be billed more for it. _Bottom line they couldn't prove it so they apologized and removed issue from his account with no changes._
Good luck to everyone. (my boss was on 4.2.1 and he is using about 25gb per month)
AT&T is hoping people will either ignore the message or call to apologize (Don't act guilty and you'll be fine)"
http://www.reddit.com/r/technology/comments/g62wv/i_woke_up_...
If this is the case, user agent spoofing will not work, and it would be quite a bit of hackery to trick iOS' IP stack into spoofing TTL's for packets from tethered devices.
these can/may be manipulated via ip-tables, but then you still have a huge data-volume to account for...
At least you'll be sure telco guys are not inspecting your packets by any means, be it "teethering detection", blocking some kind of traffic, or something more malicious, like profiling your Google searches. (Timing analysis may still apply.)
With GNU/Linux iptables it's just one rule in the "mangle" table with TTL target.
On *BSD with pf "packet normalization" can be done with pf's "scrub" directive with min-ttl option.
Unfortunately, I've never used iOS and/or OS X/Darwin, so I don't know what are possibilities are there. But I believe there should be some.
(Edit: on reflection, if you know enough to know about the forwarding chains, I'm sure you know that TTL is 8 bits. Sorry.)
I was talking about modifying TTL of the forwarded packets on the phone, to make the packets look like they were originated from the phone itself.
As a bandwidth user (=carrier customer), I don't think it should matter.
As a bandwidth provider (=carrier), I would probably think that different use cases provide different levels of value to the customer, and thus can motivate different prices.
You might argue that bandwidth to a computer is "more worth" than bandwidth to a smart phone, since the computer has more power do to things with that bandwidth. That also means that, to a first approximation, customers can just plain use more bandwidth from a computer, which of course also makes it interesting to charge more for the ability to do that. And so on.
Good luck suing them. They offer tethering for a price, you're not paying it. I think the chance you'll get away with invasion of privacy on something that they technically should only see from flagged account is about 0.