European telecom operators have rolled out voluntary measures to help Ukrainian refugees and expats in Europe. These include actions on free/reduced calls and SMSs in 31 countries, free/reduced outbound roaming in 29 countries and SIM cards for refugees in 21 countries.
Additional measures include: wifi hotspots at places of arrival of refugees; boosting mobile signal in border areas and a range of other humanitarian measures.
A non-comprehensive list is available at this link. It has been prepared by Cullen International and is updated on April 1st 2022.