internet service provider & connections

[Maged Roshdy]

hi ranchers
could anyone help my to understand the problem in my chatting program
1. in my chatting program i have to peers client and server
2. evrey client have a list of frends when he click on any of them he
starts a private chat with his frind.
3. when the client click on his frind name he retreveis his ip from the
server and the try to connect to his frind (now his frind will act as
server and he will act as client)and start a private chat.

this program is working properly on the LAN but when i use the WAN the
the private chat unforunaitly ain't work and the client(Socket) couldn't connect to his frind (ServerSocket).
i guss that the public chat works becouse the server have a real IP (fixed)
but clients connecting to the internet by an (ISP)internet service provider
so they don't have an real IP for other client to connect on
plz if i thinking true tell my if there any solving to my problem if not
tell my why my program doesn't work on WAN
thanks in advance..