Nick, have you tried to use the test feature?

I know you are looking for intercom tone, but you'll never find a real good way except to have a digital set with you, the best way is to just type in: test station xxxx where xxx is the station number. or try using status station xxxx this will tell you if the port is connected to a set or not, I usually just take it from the jack and walk it over to the wall field and connect it to see if it's the cable or the port or the phone.