Wi-Fi calling is a fairly new mobile phone feature which allows you to make phone calls, send texts over Wi-Fi rather than the more traditional route; using your mobile network which uses the masts.
It is to improve connectivity and coverage because rural areas tend to have patchy reception.
Wi-Fi calling will need to be enabled on your mobile phone device and then it will be able to link in with any connected wi-fi network. Once enabled, most networks allow you to move between wi-fi calling or via their network automatically.
How to make a Wi-Fi call
Wi-Fi calling isn’t automatically enabled on smartphones. To turn yours on:
On iPhones go to Settings > Cellular > Wi-Fi Calling and then toggle on Wi-Fi Calling on This Phone.
On Android, Settings > Networks & Internet > Mobile network > Advanced > Wi-Fi Calling, where you can then toggle on Wi-Fi calling.
Once you activate Wi-Fi calling, you can call and text as you normally do and your action will be automatically routed through in the background.
Does my network offer Wi-Fi calling?
All major mobile phone networks offer Wi-Fi calling.