I remember the facetime announcement including that they were going to publish it as an open standard, and I'm not the only one:

  "The company said it plans to make FaceTime an open industry standard, potentially allowing 
  communication with other devices." 
  -- http://www.appleinsider.com/articles/10/06/07/apple_announces_open_standard_facetime_video_chat_for_iphone_4.html

and it's not just AppleInsider - that's just the first non-wikipedia hit for the search "facetime open standard". That said, they never (to my knowledge) delivered, which is a shame. At least now there's something, though it's a pity that FT users will likely be left out.