Most mobile phone users will still have to wait some time for Internet telephony company Skype's mobile service because of technical hurdles and a lack of suitable handsets, Skype's chief executive was quoted as saying in a Finnish newspaper on Thursday. Skype is working on being able to offer the service to the biggest mobile phone makers and for the Symbian operating system used by Nokia , among others, Skype chief executive and co-founder Niklas Zennstrom told Helsingin Sanomat.

But he said: "We have no publicly available products yet to offer and I can't give you a timetable."

"When we begun developing the mobile phone version we didn't realize the number of technical obstacles. It is challenging and is taking much longer than expected," he added in an interview with the daily.

It had intended the service would be available for handsets made by Nokia and others last year.

Skype has a version available for some mobile devices that use Microsoft's Windows Mobile operating system but these are only sold in fairly low numbers in Europe.

Launched as a free software download in August 2003, Skype offers free computer-to-computer voice calls. Only calls to or from non-Skype customers -- and any extra services -- are charged for.

Many mobile operators have seen Skype as a threat, but Zennstrom said the firm was trying to work with them, and that cooperation with his company could also be a way for smaller operators to challenge the dominant players.