FYI, I spoke to someone at T-Mobile about the speed restriction.
This theoretically applies, but apparently there is no way of doing this on phones - it is done apparently on the usb dongle thingi's.

He also said if you go over significantly they will alert you, and I assume things will escalate from there.
But if you are using it that much you should be on their top tier anyway. It seems like it is real "fair use" which is why I opted for it over the other providers.