Originally Posted by Yaatri

sometime ago, I had started a thread about unlocking a pre-paid T-mobile phone, for which I had paid full price. The thread quickly went off topic, suggesting that it was wrong to expect to have a prepaid phone unlocked.
I have a definitive answer based on my experience, which concurs with T-mobile's policy. I hope it will help those who are unsure of what T-mobile's unlocking policy is.

In the past two months, I have had three T-mobile phones unlocked. The first two were pre-paid phones, and were returned. The last one was a postpaid. T-mobile does impose one unlock code per number every 90 days. But if the phone for which T-mobile had provided an unlocked code has been returned, T-mobile will provide unlock code for another phone with the same number if it has been purchased from T-mobile or its authorised dealer.