So is this an unlocked HTC (purchased through HTC unlocked) or is it an AT&T HTC U11 that was then unlocked?
The unlocked purchased from HTC should support it.
IF its an AT&T that was unlcoked my guess would be yes but just my guess.
Mods might move this to HTC u11 forums since its device specific.
Will TMO support VoLTE on unlocked HTC U11 for AT&T?
I think there's some confusion... There isn't an att u11 only unlocked and Sprint
In any event, I've seen on XDA that the unlocked U11 works flawlessly on T-Mo.... VoLTE and WiFi Calling.