Hi all. I apologize in advance if I have created a new thread of an already existing one. This is truly my first time ever using a forum for help. So here is my problem: Bought an AT&T S4 off eBay around May 2013. Then purchased an unlock code off eBay which worked perfectly with T-Mobile. Around January 2014 the phone's Wi-Fi stopped working. Phone still had 1 year manufacturers warranty active, so I sent it to Samsung. The phone's Wi-Fi was fixed and the PBA was replaced. Phone was restored back to factory as if purchased brand new. When turned on with T-Mobile SIM inside, it asked for the unlock code. I entered in the same unlock code purchased before and it says unlock code unsuccessful. (All of the internal specs were the same, i.e. the IMEI & Serial Number.) After hours and days and now months of trying to fix the problem with both Samsung's and AT&T's ignorant and stubborn customer support I have come here. To remove all suspicion that the unlock code I bought was faulty, I had my cousin request an unlock code directly from AT&T. After 1 month of him using the S4, the unlock came in. And surprise surprise, it was exactly the same as the one I had previously purchased. Can anyone help? Please keep in mind that I would rather not root the phone to get it to work with T-Mobile.