@Handy1 one more to add. Lucky currently offers its customers to use the apps to make calls using the phone number they have. However, that is just a VoIP calling (like TextNow or Fongo) and not Wifi Calling. AFAIK, no tier 3 providers are offereing Wifi Calling at the moment
Advantages for Wifi calling is that after it is enabled and setup on your phone, it is seamless to the customers. You make calls and receive calls on the same dial pad as you always use. Customers don't need to know if the calls was routed on the carrier network or your Wifi. This is especially useful when you have weak 3G or LTE network or none, like rural area, when calls were not able to reach you on the network, the calls will then go through your Wifi instead
