This weekend EE dropped a carrier settings update to become (what I believe to be) the first carrier outside the US to support iCloud Wi-Fi calling.
They are branding it "EE smart number technology".
This means that you can make and receive calls and texts on your other iCloud-connected devices, even when your iPhone is not on the same Wi-Fi network.
However, to send and receive SMS text messages your iPhone must be switched on and connected to the carrier network, either by cellular or Wi-Fi Calling (much like the cellular Apple Watch).
They are branding it "EE smart number technology".
This means that you can make and receive calls and texts on your other iCloud-connected devices, even when your iPhone is not on the same Wi-Fi network.
However, to send and receive SMS text messages your iPhone must be switched on and connected to the carrier network, either by cellular or Wi-Fi Calling (much like the cellular Apple Watch).