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We all marvel at Facebook and its number of users, which at last check stood at around 400 million. For context, consider Skype, which at the end of the fourth quarter of 2009 had 560 million registered users, a data point Skype’s chief technology strategist, Jonathan Rosenberg, shared with the attendees of the eComm conference currently under way just south of San Francisco.

Skype, when it was still part of eBay (s EBAY), issued quarterly updates but those have now stopped. Nevertheless, here are the latest numbers:

Skype added 39 million registered users in the fourth quarter to end the year with a total of 560 million.

The number of Skype-to-Skype call minutes totaled 36.1 billion in the final three months of 2009.

Skype users made more the 250 billion minutes worth of Skype-to-Skype calls from the time the service was launched through the end of 2009.

Skype in 2009 accounted for 12 percent of the world’s international calling minutes, a 50 percent increase over 2008 when it accounted for 8 percent of international calling, according to TeleGeography Research.

36 percent of Skype-to-Skype calls as of the end of the fourth quarter included video — in other words, Skype is going to figure prominently in the video conferencing business, challenging more established players with its no-cost solution. Skype CEO Josh Silverman in a guest post for GigaOM explained why he views video as the future of Skype.

Here are some other random Skype stats:

At peak times, 23 million users are logged into Skype (as of March 2010).

Skype is available in 29 languages and is used in almost every country around the world.

35 percent of Skype users utilize it for business purposes.