I totally get the need for wi-fi calling having lived with one bar in my garden and zero in my house.
But just so not to get everyone over excited, when the service launches it will be dependent on what handsets are supported! With iPhone its notmally iPhone 5S and above for wi-fi calling and 6 for 4G calling runnign the latest iOS
And providing your handset can do both, Wi-fi calling and 4G Calling will work together anyway
Will 4g calling work on band 3 and band 20 ?