I was in MH in December and put a Vi SIM in my OP6 to test VoWiFi. I couldnt see any changes (WiFi calling button) then. I am back in Bangalore and last week saw that the WiFi calling button is enabled. I tried switching the phone to aeroplane mode with WiFi on. the phone doest use VoWiFi. fingers crossed.
Vodafone Idea or Vi has now rolled out the services in Delhi circle after introducing WiFi calling or Vo WiFi services in Mumbai, Kolkata, and Gujarat circles. The service is now available in 5 circles.