Most all of my Nokia S60 devices have a forward facing camera designed for video calling and unfortunately this is a functionality that has not been readily available or supported in the U.S. I think there have been a couple demonstrations (AT&T Video Share), but the U.S. wireless data networks can't support a consistent download/upload service like this yet. You also need to have both parties with compatible 3G phones and data plans and in the U.S. the large number of device owners and high speed data customers just aren't there yet.
The obsidial blog posted an interesting thought about AT&T's plans to upgrade their network to fully support HSPA (combo of HSDPA and HSUPA) as they release the 3G iPhone in the very near future. HSUPA is the high speed uplink part of the network and by upgrading their high speed network to support this functionality the author mentioned that video calling may finally be coming to the U.S.
We have seen different rumored photos and mockups of the 3G iPhone and some have had a small forward facing camera so this is a possibility. I haven't seen the numbers on how popular this is in Europe and other countries, but something like this could make the 3G iPhone distinctive from other devices and may get even more people moving to AT&T and the iPhone. I can see this being great for people with kids or pets who want to share live video with others, but I don't think there is too much of a need to watch the other person you are talking with on a phone conversation.