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I reserved and purchased the AT&T 6S Plus Yesterday device only and when I plugged into iTunes, I got a message telling me that my phone is unlocked. I tested with the Verizon sim on my iPad and it works.
Did you set up as new phone? I didn't see that or any unlock message when I plugged in my phone to restore from backup.
 
It's worth pointing out you don't actually need to restore the iPhone in iTunes. It is unlocked out of the box as long as you paid full price from Apple or used the Apple Upgrade Program.

I know that and you know that but they're asking for confirmation that it is unlocked. That is the only way they will get confirmation without testing the phone with another SIM card.
 
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