Internet telephony firm Skype has promised to expand its range of free and low-cost voice over internet services with the launch of a video calling offering in the new year.

Niklas Zennstörm, Skype chief executive and co-founder, said today that the company was currently testing a video-over-IP service.

"We can easily develop new services on top of Skype," he said. "One is video and we are expecting to deliver something next year."

He added that the firm was able to deliver a video offering currently, but was continuing development to ensue that service quality was acceptable.

The operator, which offers free or low-cost voice calls by routing traffic over the internet, also announced that it was developing software that will allow its voice offering to be used on next-generation smartphones.

"In April we released Skype for Pocket PC. The next step will be Skype for different types of smartphones. We are currently evaluating different smartphone operating systems including Microsoft, Symbian, Palm and Linux," said Zennstörm.

He acknowledged that the firm may have made a mistake in underestimating the fast-growing market acceptance of IP phones conforming to the Session Initiation Protocol (SIP) standard which effectively allows IP calls to be automatically routed to compliant handsets.

"We may have made the wrong decision. We looked at the whole SIP standard and saw problems with it," said Zennstörm. "We developed proprietary technology to solve these problems."

He went on to claim that most Skype customers were not currently interested in making voice over IP calls to SIP-enabled handset users.

"We take great care to listen to our subscribers and, so far, making calls to other SIP-based voice users is very far down their lists," said Zennstörm. "It is not on their lists therefore it is not on our lists."