Service independence in online applications

One of the things that all the internet-enabled applications need right now is service independence. This is to say that the way we connect to a certain application should have no effect on who we can communicate with. As in email, if you're using Hotmail or even your local ISP's mailbox, you can still communicate with any other mailbox. Why not the same with IM or voice chats? IRC started this sort of thing but didn't get too far. The different networks still remained separate even though servers did collaborate to allow users to communicate with other servers' users. Google's shown the intention to pursue this with their proposed sevice independence with Talk. We can only hope that Microsoft and AOL (among others) create a scenario together where an MSN user would be able to communicate with a Google or AOL user regardless of the client they're using. With Microsoft and others going for improving voice capabilities to hold their market share, this needs to be addressed as much as VoIP. What do I care if my friend's using AIM or Talk? I just want to have a conversation.