First and foremost we have a mailing list where most stuff gets done. Or at least discussed. One of the lessons we learned from being three separate teams that had many channels of discussion is that that model doesn't work well. Therefore, all important discussion happens only on the ML. No IRC meetings. Everything is documented and sent to all team members.
We have an IRC channel where we can discuss certain issues, but there are no scheduled meetings although we meet on occasions. Team members are too spread out across the globe for that to work well, so IRC discussions are kept to a minimum. This way, all the important things are on the mailing list, and it is assumed that everybody on the team sees it.