How to make video calls?

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I have a webcam and broadband internet connection like most people nowadays, I want to call somebody who has a mobile phone with video call support, how can I do that? My mobile phone (BlackBerry) doesn't support video call and has no front camera, so phone to phone is out. Do I have to use an ISDN phone or is there an alternative? I know there's Skype, Gizmo5, etc, these services offer voice calls to phone numbers, and video to PCs, though I'm not sure if they support video to phone numbers. Can someone recommend a good service? I don't mind paying for it.