Found in the manual for the new Airport Extreme (of which I am anxiously awaiting) is this tidbit which might help us iChat users out there:
You can set up NAT Port Mapping Protocol (NAT-PMP). NAT-PMP is an Internet Engineering Task Force Internet Draft, an alternative to the more common Universal Plug and Play (UPnP) protocol implemented in many network address translation (NAT) routers. NAT-PMP allows a computer in a private network (behind a NAT router) to automatically configure the router to allow parties outside the private network to contact this computer.
Included in the protocol is a method for retrieving the public IP address of a NAT gateway, allowing a client to make this public IP address and port number known to peers that may wish to communicate with it. This protocol is implemented in current Apple products, including Mac OS X 10.4 Tiger, AirPort Extreme and AirPort Express networking products, and Bonjour for Windows.
This could prove very interesting indeed.