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I had a ZTE ZMAX Pro unlocked through MetroPCS back in November after 90 days of consecutive service. Everything was fine until about a month ago, I had a warranty repair done on my phone and it was returned to me factory locked again. The Unlocker App displayed that my phone was Permanently Unlocked, but I kept getting an invalid SIM error when I had my other SIM in. After talking with both ZTE and MetroPCS support (of course, they each pointed the finger at each other), I ended up sending my phone back a 2nd time to ZTE and contrary to my instructions, they replaced it with a brand new (still locked) phone. Now that the IMEI number has changed, MetroPCS can't unlock it since that phone never had service with them. Omar from MetroPCS support (ID# 12351) shockingly suggested I use one of the paid unlocking services to get my phone unlocked. Based on Omar's suggestion, I did attempt to use one of these paid services, but my money was immediately refunded, as the service was unable to find the IMEI number of my new phone in their database. I now have a perfectly working wi-fi only phablet.
In hindsight, I think, had I not restored my data to my original phone, I might have been able to use the unlocking app to request a 2nd unlock, but I'm not sure. When I restored data from my old ZTE to the 2nd (new) phone, the Device Unlock app now thinks the device is unlocked and has the history from my first phone there. In other words, my brand new warranty replacement phone thinks it was unlocked prior to its manufacturing date (which is impossible)! I had not given this much thought on my first phone since I figured it had retrieved the unlock history from the MetroPCS server. I did a factory reset on this phone, and got the expected "Device not authorized to unlock" message after clicking on the (now available) "Permanent Unlock" button. So, something with the backup and restore process made both phones think they were unlocked.
If there's any way ZTE can send/trade me back my old phone so I can try the steps above (nobody suggested I factory reset the phone without doing a restore), I would be grateful; otherwise, I fear I'll have to activate this phone with MetroPCS for 90 days in order to get this phone unlocked. I had a friend with an iPhone - same issue, and Apple did a warranty replacement with an unlocked phone. Why can't ZTE do the same when the device being returned is already unlocked through legitimate means (by MetroPCS)?