Before the iPhone came to light, very few people surfed the web using their mobile phones even though basic mobile browsers were existent. Today, the numbers are staggering. It's all about the UI and speed of the iPhone's browser, which many platforms are now just catching up too (android and blackberry).
Can the 4th iPhone do the same for video calls?
Video calling hasn't picked up speed even though it's around for more than 5 years, Nokia always was against this technology because their tests showed that no one is really using it.
If Apple will incorporate a front-facing camera, which rumors say they will, what would be their magic ingredient?
A camera shutter switch.
Moving from voice calling to video calling should be easy as flicking a switch. once a call is in progress, and both sides have a video-call capable iPhone, the shutter on the front-facing camera would light up. to "add video" all you will need to do is move the shutter switch and immediately the other side will see your face, then they will here a beep and will be encouraged to do the same when the light on their shutter would light up.
Plus a faster 4G network couldn't hurt...