I have contacts on my address book that has an iPhone and they use FaceTime. When Yosemite officially got released last October. I noticed that the FaceTime is greyed out on my contacts that have iPhones. Later on this problem got solved. I would go to FaceTime and started doing a search on my contact list and that solved the problem. I know that the El Capitan is still on beta but hopefully apple would fix this problem.