I'm using Instant Messaging for (second level) tech support more and more, and it's great for this purpose:

Interaction is just so much faster than with e-mail exchange, and it's not dragging my attention as far away from my current work as phone calls do. I can send text, URLs, files...

Two things we're used to having with plain old telephony still seem to be missing, though:

How can I setup an IM account that points to a group of people and connects me to the first one willing to accept a message? (Which would be just the way that help desk phone numbers are working.)

Secondly, how can I put someone through to another IM account when I find out - during the conversation - that there's someone more able to answer the question? I can do this easily with the phone. Well, there is an IM workaround: But inviting someone to a group chat and then leaving the chat is just not as intuitive (or am I just stuck in a telephone perspective?)...