Keeping a group in sync is also possible (and I'd say preferable) via email, since current objectives and sprints don't change very quickly at all relative to the speed of conversation, and both have natural paper trails. But if your current objective is something like triaging a complex outage or live event, IM works beautifully for that.

I've done remote work via long conference calls before and it works for certain types of work; I agree that IM is much more preferable.