High data charges are stopping the mobile version of Skype from becoming more widespread, according to the company's head of business development. 

The release of a download version of the Skype software that works on Nokia 3G phones had fuelled speculation that the software would be ported to all mobiles. 

However, Skype's Eric Lagier maintained that the ongoing development of the software will be hampered if network operators fail to offer cheaper flat-fee wireless broadband packages.

"We do not want to be in a situation where we say 'Skype is free' and then at the end of the month the user gets this huge broadband bill," Lagier told Reuters.

Pete Cunningham, an analyst at Canalys, added: "The market is not really ready yet and there are a few things restricting its uptake, tariff being one of them." 

The £5 monthly tariff from network operator 3 for unlimited internet access is one example of a service that could help drive VoIP use on mobile phones.

"3 is taking a step in the right direction and is putting pressure on the other operators," said Cunningham.

However, the analyst warned that VoIP services need to address some problems before they become standard.

"There are issues around quality of service, and the handover between mobile Wi-Fi connections needs to handled better," said Cunningham.