This procedure will force activate iPhone. If it is after the official unlock from the operator T-Mobile USA, when you activate a new status through iTunes prompts you to specify the ZIP code (Billing Zip code and Last 4 SSN (Last 4 digits of Social Security Number).
ATTENTION! VERY IMPORTANT:
Unlock new models SE/7/7+/8/8+/X is more expensive. Look price in the drop-down selection list of models.