Just by means of some background info with any MVNO of which Virgin Mobile is one. MVNO = Mobile Virtual Network Operator, or a "piggyback" provider in common parlance.
Whichever network operator provides the underlying coverage makes no difference to additional services such as WiFi-calling, as you are not a customer of VF or EE. You're a customer of Virgin Mobile, and it's the services that Virgin offer that matter to you. The fact that Virgin happen to use xyz network for their radio coverage, is irrelevant for this particular query.
If you want to avail of a particular service offered by Vodafone or EE, then you should be a customer of those operators directly.
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