Sorry if this has already been answered but are the servers international ???
What do you mean "international"?
You can join pretty much any server as long as it's a PC server, or X-Box server etc..., unless it's password protected, then you need the password, obviously. :D
I assume that "Session is full" is the same as max players have been reached and the room is full, right? I get it all the time while trying to use Gamespy Arcade.