More threats for European mobile operators from EU Telecoms commissioner Viviane Reding—this time she’s told reporters at the Mobile World Congress that operators must introduce “credible” cuts to the price of texting and surfing the mobile web while abroad in the European Union, according to Reuters.

Reding: “Sending a text message or downloading data in another country should not be substantially more expensive than at home.”

She added that operators had to tell customers by July 1 how much they were charging them for mobile data roaming.

In January, Reding warned that she was watching developments closely in mobile data roaming and would respond “appropriately” if she didn’t see any progress made at the end of 2008. A number of operators have already reduced data roaming charges, including Telefonica/O2 and Vodafone (NYSE: VOD). On Thursday, five European operators--Three in the UK, Italy, Ireland, Austria, Sweden and Denmark, along with KPN in the Netherlands, Belgian operator BASE, German operator E-Plus and Poland’s Play—agreed to cuts, while Telia Sonera announced today it would reduce charges as well, but did not clarify the exact pricing. 

• Five European Operators Cut Mobile Data Roaming Charges
• T-Mobile Working To Reduce Data Charges; Vodafone CEO Says No Regulation Needed
• Ofcom Takes Aim At Pricey Mobile Data Roaming Charges
• Reding Looks At European Roaming Data Charges