In the latest iPhone SDK - a collection of resources used by developers to build applications for the platform - hints have been uncovered that strongly suggest that a future version of the iPhone, iPad or iPod Touch may arrive with video calling functionality.
The files are found in the TelephonyUI.framework directory - indicating that they consist as part of the interface for the functionality. They're titled "AcceptVideo_SatFeb20_s1...2010.png" and "DeclineOrEndVideo_SatFeb...2010.png" and the icon shows a video camera of some sort. Within the apps, there's also reference to "VideoChat" in the UI.
As 9to5Mac points out, it's possible that this code has been brought over from Mac telephony products, but it would be unlikely that icons would have been created and compressed into the SDK if this wasn't planned to be appearing in the iPhone or iPad at some point. It matches up nicely with front-facing camera rumours, too.