Per current US Law, unlocking your phone from your current or former cell-phone carrier can only be done by the carrier themselves (unless the phone was factory unlocked to begin with). There are certain criteria for each of the major carriers.
SellPhoneCentral may pay extra for your unlocked device so it may be worth your time to unlock the device before selling it to us.
Please note though that if the phone received is not unlocked for the carrier at time of receipt, we will only be able to honor locked pricing.
For full requirements on how to SIM Unlock your T-Mobile phone please click here
If you meet all their requirements, you will need to contact T-Mobile to unlock your device.