AT&T and Samsung are both notoriously bad with Android updates, but they've done a good job with this latest update for the Galaxy Note5 and the Galaxy S6 edge+. Not only does this update bring the latest security update, but it also adds support for AT&T WiFi calling and Advanced Messaging.
AT&T started rolling WiFi calling out back in June with the LG G4. It hit the Galaxy S6 active nearly three months ago, the Galaxy S7 and S7 edge about two months ago, and the LG V10 a month after that. It's kind of odd that a niche phone like the S6 active got the feature so far ahead of the much more popular Note5, but at least it's here now.
Also included in this update is the September security patch. Considering that the AT&T Galaxy S7 edge still doesn't have this (and neither does the T-Mobile model), this is fairly impressive. (Bonus tidbit: the AT&T Galaxy S5 got the September security patch before any of these.)
The update should be rolling out already for both the Galaxy Note5 and S6 edge+. It comes in at a size of between 405 and 436MB depending on your current software version. The baseband versions for the Note5 and S6 edge+ are N920AUCU3CPHA and G928AUCU3CPHA, respectively.
The Galaxy S6 has also received an update that includes WiFi calling and Advanced Messaging, but only the August security patch is present. No sign of any update for the S6 edge yet.
The update is rolling out to the S6 edge as well now. Like the S6, it only gets the August security patch.