AT&T started rolling out WiFi calling to some of its devices a few months ago, starting mysteriously with the LG G4. The GS6 Active and LG K10 followed that, but now a pair of newer flagship phones finally have it too. The Galaxy S7 and S7 Edge are getting WiFi calling in the latest OTA.
The new update starts its rollout today (build AUCU2APG1), and will include the following.
Setup and Transfer
AMBS Phase 3
Yeah, so that's pretty lackluster other than the WiFi calling. IPME is AT&T's advanced messaging standard, which won't do you much good right now. The setup and transfer item presumably means that feature is getting tweaked. As for AMBS, that's probably AT&T Messages Backup & Sync. Again, not a big deal.
The update will just shy of 600MB, and you'll need WiFi. Make sure the signal is good because AT&T only lets to try to download an update once per day.