The European Commission has set up a website to help people cut the high cost of using mobile phones abroad.
Compare mobile phone roaming charges around Europe
The Commission says the site reveals the tariffs of all mobile operators in the European Union's 25 member states.
It also gives sample comparisons to illustrate the wide variation in charges for 'roaming'.
The Commission says the cost of using a mobile abroad "is hard to believe" and hopes that greater transparency will lead to lower charges.
In July, according to the Commission, consumers faced charges ranging from 0.58 euro cents to over 5 euros per minute.
According to the website, British tourists in Italy are charged 50% more for mobile calls made and received there than French tourists.
By giving consumers more information, the Commission hopes the website will give allow mobile users to change their mobile habits and save money.
It suggests people could sign up for cheaper holiday tariffs offered by some operators, change their mobile operator altogether, or buy a foreign "pay as you go" SIM card to avoid the increased cost of making calls abroad entirely.
"The Commission aims to give the consumer the knowledge to make an informed choice, to enhance competition in the industry and to encourage fairer and clearer pricing," EU information society and media commissioner Viviane Reding said.
The website will be updated every six months. As well as sample tariffs it also contains links to the full tariffs of every operator in the EU.
The high cost of roaming charges has been examined by the Commission since 2000. It has already accused mobile phone companies in Germany and UK of charging excessive wholesale tariffs to other operators.
Since December, national telecom regulators in the EU have been working on ways of regulating the tariffs charged to retail customers.