The EU Roaming Regulation applies to the 27 EU member states: Belgium, Bulgaria, Denmark, Germany, Estonia, Finland, France, Greece, Ireland, Italy, Croatia, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Austria, Poland, Portugal, Romania, Slovakia, Slovenia, Sweden, Spain, the Czech Republic, Hungary, Cyprus and the so-called EEA states of Liechtenstein, Norway and Iceland.
Since Great Britain left the EU, applies to this country Not more the EU Roaming Regulation. According to information for customers of the providers Telekom, Vodafone, o2 and 1&1, nothing is changing at least at the moment. In some cases, however, the providers are limiting their accommodation until the end of 2022. Before you travel, find out from your provider about the current conditions.
Danger: The EU roaming regulation only applies to the countries listed (i.e. not to Switzerland or Turkey) and not to the mobile phone networks of airplanes and ships.
The EU Roaming Regulation does not apply to San Marino, Andorra, the Isle of Man, the Channel Islands, Gibraltar, Vatican City and overseas territories in the Caribbean. Some providers still assign these areas to the EU country list, but others do not. So be sure to check before you travel!