Can I use the mobile phone camera as a computer webcam

Well, it seems that the answer is that there is no such app, because - sadly enough - Apple did not implement the complete UVC protocol.

Here is a webpage where some people describe their findings, and try to implement the UVC protocol. It did not work with my own cam (Microsoft HD 5000), but it might work with others...

http://www.phoboslab.org/log/2009/07/uvc-camera-control-for-mac-os-x

From a quick look at the specs, it seems to have a composite A/V output, like my Canon Ixus, which you could connect to a video capture card (like an old analogue Hauppauge WinTV card). Some software, like Windows Live Messenger, for example, can use that as a webcam source. There also appears to be an HDMI output, which would be easier to connect, but I do not know if any chat clients can use that as a video source. It all depends on what you are trying to do.