Skype has 145m monthy users

"With 145 million average monthly connected users for the fourth quarter of 2010 and 29 million concurrent users at peak times, Skype’s reach and engaged user base makes it an attractive platform for brands to market their products. The first advertisers to sign up with Skype include: Groupon, Nokia, Universal Pictures, and Visa."

Source:  Press release from Skype, 7th March 2011