The European Commissioner for Information Society and Media has expressed concerns about data roaming charges across Europe and wants to see significant price cuts.

Viviane Reding has already succeeded in cutting voice costs, and now wants reductions in data costs by 1 July. She has threatened mandatory requirements if her calls are not met.

Vodafone has already cut prices voluntarily by up to 45 per cent in an effort to keep regulators at bay.

"Higher roaming charges abroad must be justified by additional costs for operators. If not, they will have to disappear," she told delegates at Mobile World Congress in Barcelona.

Reding added that current pricing policy goes against the open market spirit of the European Union.

The Commissioner did differentiate between relatively mature data markets, such as for SMS, compared to newer services like mobile messaging.

But in some cases customers are being charged €7 per megabyte for data that costs 25 cents to deliver.

Mobile phone customers should also receive better warnings over data and voice costs. Reding pointed to cases of users inadvertently racking up thousands of pounds worth of charges.