Facebook and Google are separately considering some sort of deal with Skype that could involve either a joint venture or an outright acquisition. According to a report in Reuters, Facebook CEO Mark Zuckerberg has taken part in internal discussions about buying Skype, a deal that could be valued at $3 - $4 billion. The discussions are said to be in early stages but apparently are serious enough that Skype has delayed its planned IPO to the second half of this year.
The two have already done some work to integrate their respective services. Currently, Skype users can call their Facebook friends with listed numbers from within Skype's desktop client, and lets them see their Facebook news feeds in their Skype news feeds, but so far that collaboration has not extended to voice and video calls from within Facebook. That would be a major opportunity for Skype considering the social network's massive user base.
Back in January a few Facebook users reported to have started seeing a Call button randomly show up when they visit their friends' profiles. The button didn't seem to do anything, but it shows that Facebook is interested in providing voice services and might build upon its previous arrangement with Skype to implement the feature on its site.
A tie-up with Google is slightly less obvious given that company already has voice calling embedded into Gmail and its standalone Google Talk client, though a possible partnership could involve anything from audio and video compression technologies to native integration with its mobile and TV platforms. Unfortunately we can only speculate until an actual announcement is made from either company -- if a deal is in the works at all.