The "legal complications" that prevented the open-sourcing of FaceTime were apparently because they lost a lawsuit [0]. Then they had to switch FaceTime to use Apple's servers for signaling/connecting instead of peer-to-peer [1].

[0]: http://www.bbc.com/news/technology-20236114 [1]: http://www.reddit.com/r/apple/comments/1xuzif/what_ever_happ...