AT&T Wireless Changes throttle limit on Unlimited Data:

I was wondering why I stopped receiving messages from AT&T about getting close to the 5GB on my Grandfathered Unlimited Data Plan. Now I see on their T&C page that they have increased the limit to 22GB before they throttle and that is only if you are in an area where the towers are congested. I don't have to worry about this where I live so it looks like my decision to keep my Unlimited Data Plan was a good one after all.

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"Reducing data speed (data throughput) and network management are common practices in the wireless industry.
As always, Unlimited Data Plan customers have the comfort of knowing that, no matter how much data they use in a billing cycle, they will pay a single monthly flat rate
That won't change. That is the essential promise of the Unlimited Data Plan, and we are pleased to continue honoring that promise. As a result of AT&T's network management practices, customers on a smartphone with an Unlimited Data Plan who have exceeded 22GB of data in a billing period may experience reduced speeds for the remainder of that billing period when using data services at times and in areas that are experiencing network congestion. Their data usage threshold will return to 22GB with the start of the next billing cycle. Even when subject to potentially reduced speeds customers normally can still have a good experience surfing the Web, accessing email, and continuing to use an unlimited amount of data each month without incurring overage charges. Customers will likely notice the biggest difference while streaming video. Streaming video consumes the most data of all activities and may be slow or choppy when a customer has used more than 22GB of data in a month and is using data at times and in areas that are experiencing network congestion.
Using Wi-Fi does not create wireless network congestion or count toward wireless data usage and can reduce the likelihood that customers will be impacted again. Smartphone customers have unlimited access to our entire Wi-Fi network at no additional cost.
Advanced notification that your speeds may be slowed down
You'll receive a text message from us before experiencing any change in speed in a billing cycle The text message will be sent each time you reach 16.5GB (75% of 22GB) so you have sufficient time to adjust your usage to avoid network management practices that may result in slower data speeds. Speeds will only be reduced when using data services at times and in areas that are experiencing network congestion. Speeds will return to normal at the start of the next billing cycle.
You receive a text message about reduced speeds
If you have a smartphone and exceed 22GB of data in a particular billing cycle, your data speed may be reduced during the remainder of that billing cycle if and when you use your phone at times and in areas that are experiencing network congestion. You will not experience any reduction in speed while using Wi-Fi."



http://www.att.com/esupport/article.jsp?sid=KB410284&cv=820