Phone work with "New AT&T" ??

[Colecaz]

In looking at cell phones I see some of them showing in their "works with" descriptions that they don't work with "New AT&T". These phones all have LTE and bands that AT&T uses and are shown to work on T-Mobile and AT&T otherwise. What is "New AT&T" that they won't work?

[zapjb]

Maybe 5G.

10char

[kevink1]

Would have helped to have an example, but maybe by new ATT they mean phones on the VoLTE compatibility list. Not that long ago if needed it could work 3G but ATT is getting stricter.