I believe laconi.ca (http://laconi.ca/trac/) provides exactly this kind of functionality. As always, though, it's a chicken-and-egg problem. Look at Jabber and how little it has taken away from the proprietary IM protocols. As long as everybody and their mother is on Skype/Twitter/etc. there's not a big incentive to switch.
Yes but there needs to be a protocol not just a competing server.
It seems like the older internet protocol standards like SMTP work better. At least some of this generation of protocols seems to have played out in horrible ways like the IM market where one or at most 4 vendors have walled gardens and an open standard doesn't win. I guess in the early 70s when SMTP was designed there weren't a bunch of big corporations looking to "monetize" every new feature, just some bearded coding gurus in academia who wanted to build something that worked.
