As 'maus42 guessed, I IRC from Emacs. I used to chat with the built-in IRC client called ERC[0], but then I switched to leaving a Weechat session running on a VPS under `screen', and I use weechat.el[1] to connect to it from Emacs. As for IMs, there's jabber.el[2], which I used from time to time to talk over Facebook messenger and (pre-Hangouts) Google Talk.
Overall, it's surprisingly convenient to talk from your text editor. The context switch is much smaller, not to mention having available all the convenient text editing shortcuts and features you're used to.
Thanks for the helpful response temporal, although I'm not sure if my productivity this afternoon is going to go up or down at finding out this new information. ;-)