Which carrier's SIM are you using? Which device are you on (SGH-T889, SGH-I317 etc). If not a T889 on Tmo, what method did you use to unlock it?
How long have you had the device? Did you get it new from Tmo/retailer? If not, have you checked the IMEI via the Tmo website?
Hastily spouted for your befuddlement