Mike,
VoLTE can be started by Phone manufacturers only via toggling it through firmware update. It's entirely up to Microsoft if to activate this feature in capable phones.
For the reason only known to them, they are not activating this feature.
People who are or rather say were loyal to Microsoft who purchased Lumia phons despite of App Gap are banging their heads and cursing themselves for their stupidity of buying Lumia phones as Microsoft is not enabling VoLTE.
This is the least Microsoft can do for their ex-loyal Customers.