Like the data?
I heard that it works on EDGE or 3G if said area is refarmed but that was about a year ago and maybe things have already changed.
Basically I'm wondering if the Nokia Lumia 900 has 3G/4G on T-Mobile.
If your Nokia Lumia 900 is free of any network lock means,it will work on T-Mobile.
Locked means,you will need to unlock it.For unlocking you can approach your service provider or else try to buy an unlocking service from any one of the online unlocking service provider like ClassicUnlocking.com