While I understand your SIM works fine..I would suggest stopping by a local T-Mobile corp. store and have them verify your network settings on the device.
The second thing would be to try a new SIM. I understand it works on another device but without knowing what type of SIM it is (which isn't easy to determine w/o the #'s on it), it can't hurt to try a new one....
The third thing it could be is settings on your account or regarding that device. Regardless, a TMobile store should be able to get you back in business.