While T-Mobile has been building a reputation as the most honest mobile carrier in the business, the company has just gotten a slap on the wrist by the Federal Communications Commission for lying to customers about the speed of their data after they passed their data cap.

Users on T-Mobile are not cut off from data completely after they pass their data cap. Instead, the company throttles users to somewhere between 64 Kbps and 128 Kbps.

"The FCC is committed to ensuring that broadband providers are transparent to consumers. I'm grateful T-Mobile has worked with the FCC to ensure that its customers are better informed about the speeds they are experiencing," said Tom Wheeler, FCC chairman. "Consumers need this information to fully understand what they are getting with their broadband service."

The speed itself was not why the FCC went after T-Mobile. Rather, it was that T-Mobile did not tell customers exactly how fast their connection was. In fact, speed-testing websites would report users had full data speeds because T-Mobile built a system where speed-testing websites were exempt from the throttling.

"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," said the FCC in a statement.

Essentially, the self-proclaimed "uncarrier" will change the language it uses in text messages and direct users to an official speed testing website by T-Mobile itself, where users can get accurate speed information about their data connections.

"Chairman Wheeler recognizes that speed-test apps help consumers make choices among competing mobile broadband services, and we agree," said T-Mobile in a statement. "The additional disclosures we're providing to consumers on this issue will be sure to prevent any confusion and are another solid Un-carrier move."

T-Mobile is not the only mobile carrier that the FCC has been going after in recent months. In October, Verizon agreed to stop its plans to throttle users on its unlimited plans. The FCC has sent letters out to all four major carriers, investigating their data speeds.

T-Mobile is, however, making it easier for users who often go over their data caps, having announced 14 music-streaming services that will not count against a user's data when used. These include the likes of Google Play Music, which has been added to a list that includes popular services such as Spotify and Grooveshark.