I recently updated all my iOS devices to iOS 8.1 and my MacBook to Yosemite. And of course I wanted to try making a phone call over the iPhone (nice feature: selecting a phone number in Safari will give you the option to call it). It didn't work. The error message was Your iPhone must use the same iCloud and FaceTime account, which was the case actually. But my phone number was not listed as You can be reached for messages at neither in Messages nor in FaceTime.
After googling a bit I found http://support.apple.com/kb/ht5538. The only option that did the trick for me was the last one. In short: sign out of your Apple ID from Messages and FaceTime on all your iOS devices as well as your mac(s) and sign back in with your phone first I suppose. Afterwards my number was listed again and I finally could make the call.