There’s been a lot of talk on and off about mobile carriers like Verizon and AT&T throttling bandwidth for customers with “unlimited” data plans. The fact is, all carriers do this in some manner, including Sprint and T-Mobile. According to the FCC, the rules they have in place say throttling can only be done for reasonable network management purposes - meaning only in times and places of network congestion. Per the FCC Chairman Tom Wheeler, this "reasonable network management" cannot be used as a loophole to enhance revenue streams.
While Wheeler has been successful in preventing Verizon Wireless from throttling LTE users, they’re still throttling 3G users. Now, he’s got AT&T under the microscope, who at least until recently seemed to be taking advantage of this “loophole.” The main reason for this coming out is because the FTC caught wind of it and is now suing AT&T.
AT&T has since revised their policy on throttling, but prior to this, customers who used 5GB of data in a single monthly billing period were throttled for the rest of the month at all times. This resulted in barely usable service most of the time, even though the customer is paying for "unlimited" data.
Naturally, AT&T denies any wrongdoing, and instead of a public announcement, they quietly updated the policy on their website. They have also promised that they would change the policy to make it more lenient before the end of 2015, but they still face potential punishment from the FTC if it loses the case filed against them.
Here’s the important parts from the updated policy:
As a result of AT&T's network management process, customers on a 3G or 4G smartphone or on a 4G LTE smartphone with an unlimited data plan who have exceeded 3 gigabytes (3G/4G) or 5 gigabytes (4G LTE) of data in a billing period may experience reduced speeds when using data services at times and in areas that are experiencing network congestion. All such customers can still use unlimited data without incurring overage charges, and their speeds will be restored with the start of the next billing cycle.
Prior to this change, policies were different between LTE and non-LTE users. It stated the following:
Customers on a 3G or 4G [HSPA+] smartphone with an unlimited data plan who have exceeded 3 gigabytes of data in a billing period may experience reduced speeds when using data services at times and in areas that are experiencing network congestion. Customers on a 4G LTE smartphone will experience reduced speeds once their usage in a billing cycle exceeds 5 gigabytes of data.
The kicker here is that customers on limited data plans are NOT throttled. So it would seem as though AT&T is/was encouraging customers to switch to more expensive plans - at least in the years after they stopped selling unlimited data to new subscribers, and as long as it is a plan larger than 5GB.