During my time inside Trolltech/Nokia, everyone was on Freenode and our internal IRC server. A lot of people were connected through a client called Quassel [0] which is basically a distributed IRC client you can access from multiple machines (-> you'd host it on a server, it stores the backlog and everything else for you).

In my current startup we have the same (internal IRC server) and we also thought offering Quassel hosting [1] is a good idea.

[0] http://www.quassel-irc.org/

[1] http://quassel.woboq.com/