"The iPhone 4 was also the first iPhone to include a front-facing camera" (wiki)
So iPhone 3GS & its Predecessors have no front-camera, then how they (iPhone 3GS & its Predecessors) make video calls like a webcam on a Desktop PC?
If they support that, then how does it work?
Do you look at the iPhone 3GS at the back when making video call? if so, suppose your friend also has video calling function then you can't see anything in the front of your iPhone 3GS??