Europe SIM cards
No more roaming charges for EU citizens when travelling to another EU country from 15 June 2017
Included countries: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the Netherlands, Poland, Portugal, Romania, Slovenia, Slovakia, Spain, Sweden, United Kingdom and EEA: Iceland, Liechtenstein, Norway.
Beware that EU roaming rules apply only to terrestrial mobile networks (all services provided through other types of radio networks, via satellite systems on board of ships or aeroplanes for instance, they are not subject to the binding price caps of the EU).
Also, many European countries which are not members of EU can have really high roaming fees (Switzerland, Turkey, Russia, Serbia etc)