No one is really sure how carriers detect tethering, so you might get away with jail breaking without any issue. I imagine if a carrier notices a large increase in the amount of data consumed they probably assume you're tethering.
Here's a bit of insight:
For all you wondering how they can tell:
All IP packets have something called a TTL associated with them. It stands for Time To Live. Every "hop" along the network from one router to the next reduces the TTL by one. When it reaches 0, the packet is dropped. This was introduced to keep routing problems from overloading the network. If for example, by some error a packet was going around in a circular path, the TTL would eventually reach 0 and prevent a packet storm.
The thing is, ALL routing devices do this. OSes use standard TTLs. For example, let's say both your iPhone and laptop use 127 for the TTL. AT&T will receive packets from your iPhone with a TTL of 127, but since the packets from your laptop pass through your iPhone first, they arrive at AT&T with a TTL of 126. They can detect a tethered device this way.
Apple uses a TTL of 64 for the iPhone, by the way. So change the TTL on your computer to "65" and there should be no problem. Here's how to do it:
1. Click Start - Search and type regedit. This launches the WIndows Registry.
2. In the registry, navigate to the following registry key [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Servic es\Tcpip\Parameters] HKEY_LOCAL_MACHINE
\SYSTEM
\CurrentControlSet
\Services
\Tcpip
\Parameters
3. In the right pane, right-click and select New DWORD (32-bit value) and set its name as DefaultTTL and set its value anything between 0? and 255?. The value sets the number of Hops or links the packet traverses before being discarded.
REPORT
+ 81
and..
Quote:
TTL is a good start. However, deeper packet inspection would reveal HTTP requests from sources other than "approved software packages" (i.e. the http request would show a browser name like chrome). Protocols other then HTTP would be equally revealing.
Deep packet inspection is expensive; so they probably look for people whom consume a generous amount of monthly bandwidth and sniff their traffic.
The only way to protect yourself would be to encrypt your packet payload, until it reached a non-AT&T intermediate node. And of course, eventually that type of behavior would be a red flag. However, they would not be able to PROVE you were tethering, they would only have a reasonable suspicion (which appears to be enough for AT&T).
