Distributed Messanging

I'm trying to design a distributed communication suite for my friends and community...where people communicate directly to each other as opposed to common messanging protocols.

it would be like jabber or aim to start but when you click on your friends name it acts a little differently:

Scenario's

1a) everyone had some kind of public ip ...

(The main server passes some ip/domainort to the client)

2) It gets more complicated when people don't have public IP's

What I am hoping is that somehow there can be some state transfer between the clients and the server.

(A)

SERVER
// \\
CLIENT CLIENT


(B)
CLIENT=CLIENT


From what I know when people connect to sites on the internet the firewall goes into some state to allow a response back to the client....

Is there any way to transfer that abbility to respond to someone else.....??

IE: have two people behind firewalls directly communicate?

If this is possible i think this kind of research could lead into some interesting projects, like dynamic servers n' stuff..
Anyways, any suggestions would be greatly appreciated.


Thanks,

Ian