WiFi Calling is a capability that enables your phone to make calls and send SMSs over a WiFi network when cellular network coverage is not favourable. For example, when you are you are in a basement, or in another country without having roaming activated. In addition, it also allows you to make calls at local South African rates when travelling abroad. Never worry about being out of reach again.
Note: WiFi Calling-enabled devices are: Samsung Galaxy S6, Samsung Galaxy S6 Edge, Samsung Galaxy S6 Edge Plus, Samsung Galaxy S7, Samsung Galaxy S7 Edge, Samsung Galaxy S8 and Samsung Galaxy S8 Plus.