Hi, I have an iPhone 5s that I purchased through T-Mobile so it is T-Mobile locked. I will be travelling overseas and I contacted T-Mobile to unlock my iPhone. They sent me a confirmation email in which one of the steps was: "If available, insert the third party SIM." and then I would get a message in iTunes saying "Congratulations, the phone has been unlocked." But I do not have a third party SIM on me at the moment, I will purchase a prepaid SIM when I go overseas. Since there is no unlock code for iPhones, I'm confused, how can I ensure the iPhone is unlocked? I tried connecting my phone to iTunes but there was no message saying "Congratulations..." Thanks!