Everyone do this with me: Open iChat (if it ain't in your Dock, it's in your Applications folder). Click on the Window menu in iChat. If you see Rendezvous, click on that; if you see Bonjour, click on that. If you're asked to login to that network, click Login.
If everyone in your organization does this, you'll all see each other in the Rendezvous or Bonjour window. I find sending quick text messages often more civlized — and always more quet — than phone intercom. I know of one office where they change their iChat status to show when they're in the office or out to lunch, on the phone, etc. …
… Guess most people I know are fairly out to lunch most of the time, but that's another story.
By the way, you can text to my AIM account s1r4real. If I'm not online, your message will be forwarded to my phone — which is easily set up, by the way, in your AIM preferences.