WiFi Calling allows you to make calls and receive calls, SMS and MMS over a WiFi network. This will be available to Virgin Mobile customers in late 2017.
You'll be able to use this feature if you have a compatible WiFi Calling phone, you're connected to a supported WiFi network and you don't have sufficient mobile network coverage to make a call.
VoLTE is another feature Virgin Mobile will be releasing later in 2017. For more info click here.