It may be open, but that doesn't guarantee adoption...to date, only the iPhone 4 makes use of it, whereas Fring and Qik already operate on multiple platforms. If Facetime does manage to catch on and other manufacturers adopt it, then the iPhone loses that competitive advantage, since there will be plenty of Android, Symbian, and Windows phones that use it. The other OSes have the advantage of being able to use other standards as well (because Apple will not allow an app that competes with Facetime in its app store).