I haven't really tried Chatterous yet so I don't know how well it works, but just from the signup page, it's exactly the sort of thing I'd love to have done myself. Sign up, get a username for email, jabber and SMS, then you can send off group messages which go to your contacts to and from all those ways of communicating. Simple and cool - like your own private Twitter.
I'd like to see it become a little more complex - like being able to let users choose among their preferred contact types to avoid duplication, but as a proof of concept? It's very cool. And see how it's using TextMarks? I *love* those guys and that API - I wish there were more startups using them to make sure they stick around.