Ask HN: I have ssh, they have ssh, how can we chat?

I don't want a dedicated client, I want to go back to the old ways of modem to modem over VT100 links and chatting that way. How can I ssh to another machine, or they to me, and we run a cli app that allows us to chat, something basic like `wall` I think would work, but I have never been able to get that to work.

I am on Mac OS X, and ideally I could do this without installing other software, using something built in.