The European Commission has issued a new warning to mobile phone operators to open up competition and cut charges to customers for using their phones abroad.
Compulsory maximum "roaming" rates were first imposed on mobile network operators two years ago to tackle what the Commission called the "roaming rip-off".
It was one of the most popular consumer-driven moves by the EU - an average 60% cut in the maximum charges operators could levy on mobile users making or receiving calls while in another EU country.
Maximum rates have been cut again since then, making mobile roaming charges 73% cheaper on average than they were five years ago when the Commission first began pressing operators to cut their rates voluntarily.
But despite the cuts, EU Commissioner for Europe's "digital agenda" Neelie Kroes says the price gap between domestic mobile charges and roaming rates remains unjustifiably high - and her ultimate aim is to reduce the gap to nothing by 2015.
"Huge differences between domestic and roaming charges have no place in a true EU single market," she said.
"We need to address the source of current problems, namely a lack of competition, and to find a durable solution. But we are keeping an open mind on exactly what solution would work."
A Commission statement added: "Retail prices tend to cluster around the EU regulated maximum price caps and the Commission considers that EU rules give operators plenty of margin to offer more attractive roaming tariffs below the regulatory limit."
Consumers, businesses, telecom operators and public authorities are being invited to give their views to Brussels and Ms Kroes will publish proposals for "appropriate solutions" next June - which could mean more legislation.
The Commission statement said: "The Commission wants all roaming customers to have rapid and easy access to competitive roaming tariffs for voice, SMS and data, where operators' prices to consumers would be more closely aligned with the true cost of efficiently providing roaming services."