Nimbuzz today launched video calling for the iPhone and PC. You can download them here:
The Nimbuzz video calling works over 3G/4G as well as WiFi. Interestingly, they are also offering video chat, which is the same as video calling except no audio. Be sure you've got good miming skills if you plan to video chat with no verbal communication! Here's a few you can use/mimic: 
The reason? According to Nimbuzz, "This feature is awesome because it allows you to see each other on networks that restrict access to VoIP calling services". Or you can just jailbreak your iPhone, and use 3G Unrestrictor to fake out the iPhone into thinking you're still on WiFi. Problem solved and no miming skills required!
Nimbuzz added that they are now working on video calls for Symbian and Android mobile phones.
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