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.

 

  http://arstechnica.com/business/2014/11/t-mobile-forced-to-stop-hiding-slow-speeds-from-throttled-customers/