Microsoftjcorbs actually, while the experience is a little finicky, users can at least answer calls now with new fw/app and hard power reset. The key seems to have been the hard power cycle. On my test device at home, i installed FW/new app, rebooted, etc., and still had issue.. but i happened to unplug it and plug it back in, and i was able to answer calls from queue. I then remotely powercycled phones at client site via switch, and fixed it for them too. Go figure. There is still a few second delay establishing the session when you pickup the handset, but at least it doesn't flake out and put call on hold. Headset with teams client on PC still seems to be the most stable option though.
The phones are new, and so is the SW, so it will probably just take a bit for bugs to get worked out.
