Skype has announced the availability of version 1.0 products of Skype for Mac OS X and Skype for Linux software, allowing users to make free, un-metered calls worldwide.

The company hopes the new software will spur continued growth for the 18-month old company to beyond the 25 million mark of users.

In just 18 months, Skype has delivered beta and now version 1.0 products for Mac, Linux, Pocket PC, and Windows - offering cross platform function to the most popular computing platforms.

"We encourage all Mac OS X and Linux users to experience the cost and quality gains with version 1.0 Skype software," said Niklas Zennström, Skype CEO and co-founder. "We thank all those who downloaded the beta products as we were developing; your support has been fantastic. We will remain committed to innovation and will continue to expand platform choice."

Skype is the leading Internet telephony product worldwide, with more than 23.9 million registered users, and more than 130,000 new users installing Skype per day. SkypeOut, the pre-paid premium service that allows users to call ordinary telephones, has more than 735,000 paying users.

The new versions of Skype include same features available in Skype for Windows 1.0 such as: free Skype to Skype calling and conference calling for up to 5 participants, cross-platform communications, rich presence and personalization features, and the pre-pay SkypeOut service - allowing users to call any landline or mobile worldwide for the price of a local call.