HD Voice is supported by most chip makers actually. Even moreso, carriers deploy IMS (IP Multimedia Subsystem) elements such as the Application layer, Media Gateway and so on being mindful that they need to be compatible with existing handsets. Devices like FLOW’s ZTE Blade A320 are VoLTE capable (as well as HD Voice over 3G) as well the rest of their handset portfolio. Devices like international versions or even US versions of Samsung’s Galaxy S8 or S9 should also be capable since all carriers have more or less standardized their method of deploying VoLTE. FLOW (in my estimation) had recently deployed an IMS core that is now handling all voice traffic in Jamaica; in collaboration with Ericsson. I don’t anticipate there being any issues with compatiblity come time for them to release VoLTE simply because Ericsson’s solution is standardized and, hence, vendor and carrier agnostic. HD Voice happens through no effort of your own (unless you go in to disable it). But I think we’re a little ways off from getting VoLTE right now. We’re getting close but some more fine tuning of the IMS core and further deployments over Radio Access Network need to be made to get VoLTE right. HD Voice over 3G however is a very near prospect.
Side Note: I think Digicel also has deployed an IMS core solution but I might be wrong. I’m lead to think they have because of HD Voice over their 3G network but they’ve yet to have deployed VoLTE in ANY market.... period.