Back when the iPhone 5 (not 5s) first came out I had it unlocked by a 3rd party. It's a T-Mobile model. It worked fine on T-Mo for months then I switched to ATT and it's been working fine on ATT for almost a year. I needed to do a restore and after restore it lost it's unlock. When I put the AT&T SIM in it all I get is the "SIM IS NOT VALID" for this carrier long message and can't even access anything. When I put an old "dead" T-Mo sim in it it comes back but obviously it is of no use. I called T-Mo and they won't unlock it since it was purchased direct from Apple (and I no longer have an account with T-Mo). Am I dead in the water with this? Any way around it. Again, it's a T-Mobile phone purchased from Apple direct for full price. Edit: The restore was done from iCloud recent backup because there was no computer backup. It's my wife's phone.