Something sounds off here because the model of the iphone 5s in the UK is different from the US. The UK version won't pick up at&t LTE.. They should not have exchanged it.
It was a 5, not 5s. Apologies. LTE worked fine when I got back to the US. It was locked at the time. Exchanged it at Brent Cross Apple Store, if you must know.
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The the UK store messed up. If you get an unlocked unit warranty replaced they are supposed to replace it with another unlocked unit. They did not.
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Yes.
I never said my old iPhone 5 was unlocked. It was AT&T locked. The replacement from the Apple Store locked to the first SIM placed in it (in that case - O2).
Again, I'm not saying the T-Mobile 6/6 Plus is locked. I'm just looking for that 100% reassurance, especially given my experience in the past, and that my T-Mo 6 Plus just shipped.