Sorry to tell this, but no. Video chat is available between PlayBooks for now. It may be available for BB10 smartphones once they are released, but there's no way you will get it working with an iPhone. You can't use Apple's FaceTime on non-Apple devices either
You can use the app ReelPortal across all three & set up a private room to video chat. Its not PlayBook video chat but an app. I dont know why people dont use it. It works fine.