A website launched today by the European Commission gives consumers advanced warning of sky-high mobile phone costs when travelling abroad.
The move is designed to expose companies exploiting "international roaming" rates and steer phone users to the cheapest deals.
National regulators as well as the Commission have been increasingly concerned about the high prices charged for "international roaming", which enables mobile phone subscribers to use their phones when abroad.
Rates charged by service providers were described as "hard to believe" by EU Information Technology Commissioner Viviane Reding.
She said: "Only a well-informed consumer is a well-armed consumer.
At a time when we have seen in Europe so much progress in other telecommunications services, the cost of using your mobile phone abroad is hard to believe.
The site does not list all the many thousands of roaming tariffs in the EU but sets out a sample of rates ravellers can expect to face in any of the 25 EU countries.
To do this, a mobile network operator needs to conclude international roaming agreements with operators in other countries -- and the "foreign" part of the cost of the call has to be paid by the phone's owner rather than the caller.
The inevitable complexities of the arrangement make it hard to keep track of how much each mobile call to home, or call received from home when abroad on a mobile, is costing.
The charges for calling home on a mobile can vary hugely -- ten times as high calling from Malta to Poland with a Polish subscription as from Cyprus to Finland with a Finnish subscription.
However, sample Commission figures show little or no difference calling the UK from Portugal, Malta, Spain or Italy on a UK subscription.