iPhone X Why can't I just pop in a T-Mobile sim into an unlocked AT&T iPhone?

[Kendo]

In the past I could just pop in the T-Mobile sim and I could use the phone normally. Now it is asking me to "setup" the device. Is there a special reason for this? I just wanted to test out my friend's T-Mobile sim to make sure my AT&T phone is properly unlocked after they granted my request.

 

[jenag145]

In the past I could just pop in the T-Mobile sim and I could use the phone normally. Now it is asking me to "setup" the device. Is there a special reason for this? I just wanted to test out my friend's T-Mobile sim to make sure my AT&T phone is properly unlocked after they granted my request.

How long ago was the unlock??? I know it took mine a full 72 hours to be fully unlocked

 

[theshoehorn]

In the past I could just pop in the T-Mobile sim and I could use the phone normally. Now it is asking me to "setup" the device. Is there a special reason for this? I just wanted to test out my friend's T-Mobile sim to make sure my AT&T phone is properly unlocked after they granted my request.

Just next through it, it doesn't actually make any changes so not sure why it even pops that screen up...