I'm also on AT&T. I will say that I'd you don't already have the correctly enabled sim card, the system will give you a 3G only one of they enable the Z2 in your account. I had to go back and get them to fake the system into thinking I siding a different model so that it would provision LTE on my account.
Other than that, turn on LTE in the settings and use the system software to download the Internet settings and you're golden.
FYI, I dealt with the same seller and have the same comments about how great he is.
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