Apple may merge iChat with iMessage soon6
This would be a pretty big move, as few major group messaging systems like this have full cross platform functionality between mobile and and PCs. Google's Huddle group messaging is only part of the Android Google+ app, and has no web option. BlackBerry Messenger is also mobile only, as are most 3rd party options like Kik, and WhatsApp. The only other fully cross platform option is Facebook, but that system isn't baked-in to most mobile platforms.
Of course, while this would be nice, it might be better for Apple to bring some FaceTime love to iChat rather than iMessage.