Thanks for the help.
Well the gateway is connected to the Internet with a Fixed IP address. I used netmeeting to make a calls to PSTN through the the gateway. I have added the Ip address of my gateways in the netmeeting advance calling. And then in the netmeeting I just dial a local number but the netmeeting coem with a message the personal you are called is able to accept Netmeeting calls.
I hope the was enough to give me further advice