Wow it works! With the iPhone "FaceTime" video call feature, video calls are only possible when both have a iPhone and are connected to a WiFi network.
But the free application "Frings" enables free mobile video calls without WiFi, just through UMTS, 3G, Edge connection. Means that with Frings video calls are everywhere now possible, only the person to call must have Frings installed and must be added as buddy in Frings account. Just tried this with a friend and colleague at work and it was working really good. Nice tool and nice feature.