This is what The Official Nexus Twitter Handle Replied

I Tried asking the same question to the official Twitter Handle for Google Nexus, and they transferred the responsibility on the Jio. as they would be releasing the update and we should ask them. NexusVerified account ‏@googlenexus @umeshrajput_ Hi Umesh. If you're interested in VoLTE on your Nexus phone we recommend you contact your carrier to ask about availability.