When T-Mobile US customers exceed their monthly data caps, they aren't cut off from the Internet entirely. Instead, T-Mobile throttles their connections to 128Kbps or 64Kbps, depending on which plan they have, for the rest of the month.

But T-Mobile has made it difficult for those customers to figure out just how slow their connections are, with a system that exempts speed test applications from the throttling. After complaints from consumer advocates, the Federal Communications Commission (FCC) investigated the issue and has forced T-Mobile to be more honest about its network's throttled speeds.

Announced today, an agreement between T-Mobile and the FCC ensures that customers will be able to accurately gauge their throttled speeds.

"As part of the agreement, T-Mobile will send text messages to customers that will enable them to more easily get accurate speed information, place direct links to accurate speed tests on customer handsets, and revamp its website disclosures to provide clearer information about the speeds customers actually experience," The FCC said.

"Currently, customers who have their speeds reduced after exceeding their monthly high-speed data cap cannot easily understand the results of exempted speed tests," the agency also said. "When these customers run speed tests that T-Mobile has exempted from data caps, they receive information about T-Mobile’s full network speed and not the actual reduced speed available to these customers at that time."

Customers need accurate information "to fully understand what they are getting with their broadband service," FCC Chairman Tom Wheeler said.

T-Mobile has to begin implementing the agreed upon steps immediately and get them fully in place within 60 days. T-Mobile agreed to do the following:

Send customers a text message once they hit their monthly high-speed data allotment linking to a speed test that customers can use to determine their actual reduced speed;

Provide a button on customer smartphones linking to a speed test that will show actual reduced speeds;

Modify the text messages it currently sends to customers once they hit their monthly high-speed data allotment to make it clear that certain speed tests may show network speeds, rather than their reduced speed. The modified texts also will provide more information about the speeds that will be available after customers exceed their data cap; and

Modify its website disclosures to better explain T-Mobile’s policies regarding speed test applications and where consumers can get accurate speed information.

Consumer advocacy group Public Knowledge commended the FCC for taking action but said it's concerned the agreement lets T-Mobile steer customers toward only certain speed test tools. "We remain concerned that T-Mobile continues to prevent its subscribers from using the speed test application of their choice," Public Knowledge VP Michael Weinberg wrote. "Why is T-Mobile afraid to let its customers test their network connection as they see fit? What results are T-Mobile trying to shield from the public? If T-Mobile is truly confident that they are managing their network responsibly, Public Knowledge hopes that they will free their subscribers to test their network connection with an application that they trust, not one that was pre-approved by T-Mobile.”

Public Knowledge complained in August that T-Mobile's speed test policy violated a transparency requirement, the only rule that survived a court order gutting the FCC's net neutrality regulations.

T-Mobile also exempts certain music streaming services from its data limits, a practice that has been criticized by net neutrality advocates while the FCC considers new net neutrality rules.

Since becoming FCC chairman, Wheeler has forced wireless carriers to unlock out-of-contract cell phones and pressured them to minimize throttling.

"The FCC has been actively investigating wireless carriers’ speed reduction practices since this summer, when Chairman Wheeler sent letters to four major nationwide carriers about these practices, including T-Mobile," the FCC said today. "In response, Verizon Wireless announced last month that it had cancelled its plan to begin speed reductions for 4G customers on unlimited plans, an announcement that Chairman Wheeler commended as responsible action by the carrier. In addition, the FCC issued an Enforcement Advisory in July warning providers, including wireless carriers, about their responsibility to disclose accurate information to protect consumers. The FCC continues to actively monitor and address these important issues."