Originally Posted by
Howard Long
AKA "Wi-Fi calling" on both IOS and Android settings, assuming, exactly as you suggest, the OP has WiFi connectivity.
Although Wi-Fi Calling has been around for 15 years or so, it wasn't rolled out until about a decade ago on most UK providers. A lot of folk are still unaware of the feature: why would they make much of an effort to publicise a feature that would impact revenue from their grotesquely inflated roaming charges?
With most providers, WiFi calling will have the same charges applied than regular calls depending on location, i.e. in OP's situation the same grotesquely inflated £2.56/minute.
This can easily be avoided by using VPNs. though.
Vodafone expressly forbids using WiFi Calling on roaming in their T&C: "
The use of Wi-Fi Calling whilst roaming is prohibited and is not supported. However, in certain circumstances it may be possible to enable Wi-Fi Calling whilst abroad and where used additional charges will apply." (source)