If you don’t mind hacking your iPhone to install third-party software, you may want to try an application called VideoRecorder. Once installed, simply start VideoRecorder and simply tap the record button and your iPhone will capture both video coming through the built-in camera and audio captured through handset microphone.
If you really don't feel comfortable hacking your iPhone, simply wait for Steve Jobs to release the 3G iPhone, which has a dedicated video camera with VoIP and video conferencing.
