T-Mobile Unlocked X, work on ATT? Question

[FoxD]

I bought two iPhone X phones. One on ATT with my information (silver) and another one to review Mobile (space grey).'

I prefer the TMobile Space Grey and want to use it. Do I just put in my sim card from the ATT silver X? Not sure what to do...thanks!

 

[WilliamG]

I bought two iPhone X phones. One on ATT with my information (silver) and another one to review Mobile (space grey).'

I prefer the TMobile Space Grey and want to use it. Do I just put in my sim card from the ATT silver X? Not sure what to do...thanks!

Did you it from Apple full price on T-Mobile? If you did, just put your AT&T SIM in. It'll work and the phone is unlocked.

 

[FoxD]

Thanks, yes, it was paid in full and seems to work fine. Is the SIM information on the box though? Meaning before I sell it, do I need to do anything special? Just take out the SIMS? Or will the new buyer have issues setting it up?