
British carrier Three has seeded a carrier settings update--version 27.1--that enables native Wi-Fi calling on iPhones.

Three previously required iPhone customers to use its free Three inTouch app for Wi-Fi calling, but the carrier settings update released on Friday introduces system-level support for Wi-Fi calls and texts under Settings > Phone > Wi-Fi Calling.
Three joins EE and Vodafone among carriers in the U.K. with native support for Wi-Fi calling on iPhones.We know that sometimes you can't get signal when you're indoors, but that shouldn't mean that you have to go off the grid. With Three inTouch Wi-Fi Calling, you can call and text whenever you're on Wi-Fi in the UK, even if there's no mobile signal.
Article Link: Three UK Now Supports Native Wi-Fi Calling on iPhone