AT&T on Thursday announced a revision to its smartphone data throttling policy, which impacts users who have chosen to retain the unlimited smartphone data plan AT&T discontinued some time ago. AT&T’s policy had been ambiguous until now, with the carrier stating simply that the top 5% of smartphone users would experience slowed data speeds until a new billing period began. It was unclear how much data a subscriber had to use in order to approach the top 5%, however, and a number of reports claimed users were being throttled after using 2GB of data or even less. Now, AT&T is clarifying that it will only begin throttling smartphone users with 4G LTE devices after 5GB of data has been used in a single billing period, and subscribers with non-LTE devices will be throttled after 3GB of usage. It has also been reported that AT&T increased the speeds experienced by users while their data speeds are being throttled, but a company spokesperson declined to comment. AT&T’s full statement follows below.

With mobile data usage continuing to skyrocket and the availability of spectrum scarce, AT&T, like other wireless companies, manages its network in the most fair way possible so that we can provide the best possible mobile broadband experience for all our customers.

How we’re managing the network only affects a small minority of the heaviest smartphone data users still on unlimited plans. Put another way, this does not impact more than 95 percent of our smartphone customers.

Our unlimited plan customers have told us they want more clarity around how the program works and what they can expect. Here’s what customers need to know:

Customers with a 3G or 4G smartphone – who also still have our unlimited data plan – will see speeds reduced if they use 3GB (gigabytes) of data or more in a billing cycle. Speeds will return to normal at the start of the next billing cycle. For context, less than 5 percent of smartphone customers use more than 3GB per month.

For customers with a 4G LTE smartphone – who also still have our unlimited data plan – data speeds will be reduced if usage is 5GB (gigabytes) or more in a billing cycle. Speeds will return to normal at the start of the next billing cycle.

Customers will get a text message from us before experiencing a change in speed.

Even with reduced data speeds, these customers will still be able to email and surf the web, and continue to use an unlimited amount of data each month.

Not impacted by this program, launched last year, are customers on our tiered data plans.

The reason reduced speeds only apply to unlimited smartphone customers is because their data usage is significantly higher than those on tiered plans. For example, in January, the top 5 percent of our unlimited data plan customers used an average of over 50 percent more data than the top 5 percent of customers on tiered plans.

Because spectrum is limited and data usage continues to soar, we manage our network this way to be as fair as possible and so we can provide the best possible mobile broadband experience to everyone.

We encourage all of our customers to use Wi-Fi whenever possible – especially when watching video, which is the most data-intensive activity.

That’s because data activity over Wi-Fi does not count against the threshold for unlimited customers that triggers reduced data speeds or against customers’ tiered data plans. Customers can find out more at www.att.com/datainfo