VoLTE/VoWifi on Windows 10 Mobile Devices
There are several AT&T branded Windows 10 Mobile devices that are h/w and OS capable Advanced 4G LTE devices (Lumia 640, Lumia 640XL, Lumia 830, Lumia 950). However, they are not being provisioned or properly implemented for IMS Registration and HD Voice.
All of those devices could and should be able to use HD Voice and WiFi calling in addition to other Advanced 4G LTE capabilities.
There are also many Microsoft branded Carrier unlocked Lumia devices that suffer as well (Lumia 640, Lumia 640XL, Lumia 550DS, Lumia 650DS, Lumia 950DS, Lumia 950XLDS, etc.) Including the 950/950XL Dual SIM Variants.
This problem needs to get worked out. Apple iPhone is a carrier unlocked device now as are many Android phones.
Microsoft and AT&T need to work together to resolve this issue for their joint customers.