After a conventional FaceTime audio call is made between two parties, additional users can be added to a call in progress. If you are a registered iOS developer, you can install the Beta version of iOS 8 on your Apple iPhone now. And even if you're not a developer, there is a way to load the iOS 8 Beta on your iPhone now, by taking advantage of a glitch in Apple's Beta delivery system.
As we get closer to the release of iOS 8, which should take place around the same time that the Apple iPhone 6 is released, more previously unannounced features of iOS 8 will probably be discovered.
source: 9to5Mac via GSMArena