We don't have a single protocol for everyone to standardize on, and we don't even have enough access to the various protocols to build a Trillian-like client that supports everything.
I thought both XMPP and SIP were supposed to solve that problem. What happened?
XMPP won. See Facebook, GTalk. The problem is, that you can (ab)use XMPP and disable some of the open parts (federation). The protocol is still the One True IM Protocol imho, but the biggest hosters suck.
I'm less familiar with SIP, but my take here is:
SIP seems to be a good thing, but then you notice that it doesn't do thaaat much and end up in hell afterwards (Okay, we've got a session. Which (open?) codecs are we going to use now?
What I'd have loved to see is jingle taking off. Give me XMPP based voice/video. The problem? For a long time Google fucked that up. There were lots of problems because of differences between the 'standard' and the implementation on GTalk. Til today the clients don't support video or audio conferences (unless you're counting the G+ hangout feature. I wonder why it is possible there, but not elsewhere. Why can't I just video call two of my friends, G+ or not?) and they still fail to support mobile phones.
Android 2.3.4 supports audio and video, but only for a limited set of hardware, because their support is tied to a specific platform. Using a different chipset (although in a powerful phone, with all hardware capabilities and Android 2.3.4? Bad luck).
So - I'd love to see XMPP win. But for now the implementation is mediocre. There's not enough support to push it, from what I can tell.
I thought both XMPP and SIP were supposed to solve that problem. What happened?