On my N900, right now, I can setup IM/VoIP accounts for: Ovi by Nokia, Skype, AIM, Gadu Gadu, Google Talk, GroupWise, ICQ, Jabber, MSN, MSN (Haze), QQ, SIP, Salut, Sametime, and Yahoo. That's with just the built-in Conversations software, plus a few, small, free plug-ins from Extras. I'm not restricted to one active account per service either. I actually have accounts on most of those services configured and active on my N900 all the time. It just works.