AT&T has made system updates available to both the Nokia Lumia 1020 and the Lumia 1520.
The 1020, in particular, is receiving the Nokia Black update, which provides a number of new features and performance improvements. The update adds the ability to lock the screen rotation, set custom email/messaging ringtones, and more easily close apps in the app switcher.
The update for the Lumia 1520 appears to only fix bugs. Both require Wi-Fi, but can be pulled down manually via the system settings.