Tweeters do it online!
One of the items on my ever-expanding to-do list is to find out the details of all the educational chats going on in Twitter.
I've relegated that task even further down the list since discovering that Simon Johnson has done much of the work already. His article, It's all about the hashtag, lists more than 25 "ed chats", including subject-specific ones. It's not definitive in the sense of listing every single ed chat in the world (which would be worthy of a Nobel Prize, I should think), but it's a pretty good place to start.