hi first check whether your samsung omnia 2 mobile is locked to network or not to check this try this method .
Switch on your mobile phone with a sim card from a network other than the network you are currently with. If you are able to use the phone, you can be sure that your phone is not locked. If your phone displays an error message saying "Wrong sim" or "Incorrect sim" or "Emergency calls only", etc., then your phone is probably locked.
if it is locked with network then you must unlock it to accept your t-mobile sim in it .codes are the best solution to unlock your mobile .to purchase codes visit theunlockspot.com here they ask you the imei number of your mobile .finally they send you codes to unlock your mobile.