Did you /etc/apf/apf -r after editing the conf.apf file?
Also as Chirpy stated the server isn't going to be listening on that port unless something is runing to accept connections. What application and reason did your client ask for the port to be opened? Are they running a program that will listen on it? Are you sure it wasn't an egress port? I have a couple of clients that have apps that query GameServers and Teamspeak servers. I have not had to open a ingress port yet other than the default ones.
I've set up APF and modified the config to open port 3000 (I'm just playing with Ruby on Rails on my server). It still doesn't seem to be accepting connections, though. Is there anything I need to do outside of /etc/apf/conf.apf as well?