Applications open ports to listen for connections. You don't open up ports for applications. Unless you're using the firewall functionality built into OS X, but it's not on by default, so you're most likely not. If the software on the remote end is trying to connect to your server, you have to have software listening on that port to respond, if you're trying to access the software on another server, it's an outgoing TCP connection, and the client opens up a connection to the remote port.
UNIX is simple and coherent, but it takes a true genius (or a programmer at any rate) to understand and appreciate its simplicity -- Dennis Ritchie