Yeah, that's what I'm using, most of the time, thanks!
I actually get better (more consistent, faster) LTE if I use "phone", instead of "nxtgenphone", not sure why that is exactly, keep meaning to ask around the AT&T forums. It's pretty reproduceable, I can get 2-3 times speeds (RSSI and similar appear about the same however) with that settings.
Neither one gives me the Advanced LTE screen you have with your 950 though, that's a provisioning thing, I'm about 99% sure anyway, and AT&T seems to be holding out til who-knows-when, to fully-feature BYOD phones.
It's an interesting thread, but I've had 75mbps LTE since I set up my phone in early February, at least in the greater Seattle metro area, I've never had a problem with LTE.
I'm actually not that bitter about HDVoice, since it's not really true VoLTE anyway, but I suspect they'll provision WiFi calling, which I could really use on the weekends, then I'll be very annoyed ;-]
I finally managed to get a GoogleVoice number though, local, and if I run their page background (slight battery hit), I can get calls via WiFi that way, Forwarded, seamlessly. Also get texts, sort of seamlessly (okay, so so not as good on the texts, I have to use their page, but it works via WiFi and my AT&T number).