T-Mobile wants its subscribers to be able to figure out the true speed of their cellular connection. To make this easier, the company has lifted all data allowance limitations on sites that test your network speed.
A network speed test can use up precious cellular data because the test has to push your connection to its limit. Plus, if you had already gone over your limit, you would be looking at your throttled speed, which is much slower than your regular speed.
T-Mobile had this to say:
"The Ooklaapplication is designed to measure true network speed--not show that a customer has exceeded their high-speed data bucket. Other speed test providers are also whitelisted."
No matter what provider you use, you can grab the Speedtest.net app here. So, how fast is your connection? Let me know in the comments.