Please note that this is not “WiFI calling” as commonly understood.
Usually “WiFi calling” refers to voice calls via WiFi over the IMS network of a provider.
It is an open standard and widely available in various phones.
Republic wireless does use WiFi and does support calls over WiFi, but it is not “WiFi calling” over IMS.
Instead it is an entirely proprietary VoIP system that is not compatible with any phone, any 3rd party implementation or even interoperable with other networks.
Republic handles the gateways from their proptierary VoIP system to other networks.
Their apps are closed source, use proprietary transport mechanisms and are not compatible with any other network.