[gte910h]

There are dozens of legit ways to automatically detect this, and dozens more if humans are involved.

Requesting non-mobile versions of sites that do not have the option

User Agent strings such as "Internet Explorer" or "Safari" in HTTP requests

Sending screen sizes via relatively common web calls

The use of UA-Pixels at all, especially when specifying large screen sizes.

Use of protocols that are only seen in desktop OS programs (ventrilo, starcraft2, etc for instance is one that should be a good detector).

[eekfuh]

There are 3rd party web browsers on the appstore and though would trigger false-positives, so they probably would't use UA.

[mattmanser]

How are any of these legit, all of that's illegal wiretapping.

[ceejayoz]

It'd be illegal wiretapping if it were the government, perhaps, but I'd imagine the standard contract with AT&T permits this.

[eli]

"AT&T may, but is not required to, monitor your compliance, or the compliance of other subscribers, with AT&T's terms, conditions, or policies"

And, of course, it's now well-known that the government WAS using deep packet inspection on AT&T internet traffic.

I would assume they're just looking at how much you download in a month, though. I don't think AT&T is worried about offending outliers using large amounts of mobile data by inaccurately accusing them of tethering.

[sukuriant]

Could you provide a link to the government using deep packet inspection on ATT internet traffic. I don't remember it/haven't heard about it.

Just curious.

[nitrogen]

Here's what a Google search for "at&t nsa splitter" turned up:

http://arstechnica.com/old/content/2006/04/6585.ars