Obviously if the UK isn't inside the EU anymore previous roaming conditions won't apply. Still, in my country there are phone companies that include extra roam

Obviously if the UK isn't inside the EU anymore previous roaming conditions won't apply. Still, in my country there are phone companies that include extra roaming by their own like Vodafone which has the EU, Switzerland, Norway, UK, USA, etc. Phone companies love increasing their profit margins by any means.