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AT&T cracks down on unauthorized tethering

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AT&T has begun to crack down on iPhone customers who use their smartphones to connect laptops to the wireless carrier’s 3G network without the purchase of a tethering plan, reports OSX Daily.

Offending customers, which includes those who use the MyWi unofficial iPHone Wi-Fi hotspot app, have begun to receive letters and text messages indicating that AT&T requires the purchase of a $45-per-month tethering plan to use the functionality in an authorized manner. If off-contract tethering use continues, says AT&T, failure to sign up for a tethering plan will result in AT&T signing you up for one, whether you like it or not.

The letter in full:

Dear [Name of Account Holder],
We’ve noticed your service plan may need updating.

Many AT&T customers use their smartphones as a broadband connection for other devices, like laptops, netbooks or other smartphones– a practice commonly known as tethering. Tethering can be an efficient way for our customers to enjoy the benefits of AT&T’s mobile broadband network and use more than one device to stay in touch with important people and information. To take advantage of this feature, we require that in addition to a data plan, you also have a tethering plan.
Our records show that you use this capability, but are not subscribed to our tethering plan.

If you would like to continue tethering, please log into your account online at www.wireless.att.com, or call us at 1-888-860-6789 Monday – Friday, 7 a.m. – 9 p.m. CST or Saturday, 8 a.m. – 7 p.m. CST, by March 27, 2011 to sign up for DataPro 4GB for Smartphone Tethering. Here are details on the plan:

DataPro 4GB for Smartphone Tethering
• $45 per month (this gives you 4GB in total, combining both your smartphone data plan for $25 and the tethering feature, $20)
• $10 per each additional GB thereafter, added automatically as needed
• Mobile Hotspot capabilities are included for compatible Smartphones

If we don’t hear from you, we’ll plan to automatically enroll you into DataPro 4GB after March 27, 2011. The new plan – whether you sign up on your own or we automatically enroll you – will replace your current smartphone data plan, including if you are on an unlimited data plan.

If you discontinue tethering, no changes to your current plan will be required.

It’s easy to track your usage throughout the month so there are no bill surprises. For example, we send you free text messages when you reach 65, 90, and 100 percent of your plan’s threshold. If you would like to monitor your account more closely, go to www.att.com/dataplans to learn about other ways to track your data usage.

As a reminder, our smartphone data plans also include unlimited usage of Wi-Fi at no additional charge. AT&T smartphone customers can use Wi-Fi at home or on-the-go at any one of our more than 23,000 U.S. hotspots already included in your data plan.

Thank you for bringing your account up to date. We appreciate the opportunity to continue to serve your mobile broadband needs.

Sincerely,
AT&T

Please update your data plan by March 27, 2011 if you intend to continue tethering

To learn more and update your plan, visit att.com/dataplans

Reach us for assistance during business hours: Monday – Friday 7 a.m. – 9 p.m. CST Saturday 8 a.m. – 7 p.m. CST at 1-888-860-6789

One of the main reasons people jailbreak their iPhones (i.e. remove the carrier-specific restrictions that come with the handset) is to use if for tethering without paying the $45 per month.

So far, reports have only mentioned AT&T contacting iPhone users, with no word whether the same applies to those customers using Android devices. Also, AT&T has not indicated that it will retroactively penalize anyone for tethering their phones without a plan.

If you’re wondering how AT&T knows when customers are tethering without authorization, here’s how it works, courtesy of Reddit.com user byu146:

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.

So there you have it — no unofficial tethering, unless you want to pay $45 extra per month for your service.