When Apple debuted FaceTime at WWDC 2010, Steve Jobs said, "We’re going to the standards bodies, starting tomorrow, and we’re going to make FaceTime an open industry standard." Skip to 3:27 to see Steve Jobs make this promise.
Now, more than three years later FaceTime remains tied to Apple hardware like the iPhone, iPad and on Mac computers.
It's not for lack of interest in an open FaceTime standard. Developer Zach Holman called Apple out a year after the promise, pointing to Skype's interest in the service.
While Google is pushing Hangouts as the way to video chat on Android, I'm sure several Android manufacturers and app makers would jump on the chance to include Facetime for Android.
Just recently a developer created a work around to let Android users send iMessages, another closed Apple standard for messaging.