HD Voice / VoLTE on Unbranded (Non-AT&T) Devices
I understand the initial roll out of AT&T HD Voice supported only the Galaxy S 4 Mini, and that additional AT&T LTE phones may received firmware updates to add Voice Over LTE compatibilty.
My questions relate to non-AT&T phones. I currently use a Sony D5803 Z3 Compact. This phone was designed by Sony to support VoLTE out of the box. My model supports LTE Bands 2, 4, and 7, giving it full hardware compatibility with AT&T's LTE network.
Once HD Voice is brought to my area, will my device automatically be able to use it? Will other customers with non-AT&T branded/customized phones be able to take advantage of HD Voice, provided their device already supports VoLTE and their hardware is fully compatible with AT&T's LTE network?