MY SOCIAL WORLD is divided into two camps: people who use instant messaging and people who don't. When I start my workday by booting up my computer, I consider myself to have "arrived" at the office when my IM program comes to life and is suddenly populated by dozens of tiny names and faces. In fact, it's sometimes hard for me to work with people who aren't on IM. Email just isn't fast enough. And the telephone is too fast. I find meetings on the phone frustrating because I can't multitask easily while talking. Sure I can check email or browse the web, but usually the person on the other end of the line notices. All those awkward pauses between sentences make it obvious that I'm only giving this phone call 85 percent of my attention. That's considered rude on the phone, but not so with IM. Sometimes I'll be exchanging a flurry of messages with a colleague on IM, but then suddenly she'll take five minutes to answer a question. And that seems normal. She's dealing with another task and will get back to me when she can, and we'll resume where we left off.

Although IM technology has been around for years, I feel like it's reached a kind of singularity where early users of "chat" would hardly recognize it. There's an entire etiquette culture that's grown up around IM, a set of appropriate and inappropriate behaviors that vary across groups of IM users.

For example, most of the people I talk to via IM are colleagues. I work from home, and so most of my human contact during the day comes via quick exchanges and meetings on IM. Nearly everyone on my IM list has their status set to "away," which is technically supposed to mean they're not at the keyboard. But in reality, most of us set our status to "away" because we're at work and don't want to be disturbed by random people or purely social messages.

That's why every time I have IM'd somebody who claimed to be "away," I discover they aren't. Acknowledging this, we add custom messages to our "away" flags to tell the truth about our status: "Work only pls" is a common message, as is "on deadline do not disturb unless urgent."

Other people will set their messages to explain where they are: "in a meeting" or "in New York" or "eating lunch." What's great about the "away" flag, though, is that it gives you plausible deniability if you don't want to talk to somebody who has messaged you. After all, you might really be away. Who knows?

For a couple of years, Sun Microsystems researcher Nicole Yankelovich has been studying the habits of people like me who work remotely. What she's discovered is that people who don't work in a physical office tend to miss out on the casual chatter and bonding that happens before meetings or at lunch. These social interactions wind up improving workflow because people come up with good ideas while chatting casually, and brainstorming is easier in an informal environment.

I think she's right, and IM is how many of us are filling in the gap. IM is our office space, where work chatter can become casual chatter. Like a closed office door, the "away" flag means "Please knock." And once you're in the office with the person, you can have a pretty interesting talk even though you're supposed to be concentrating on your work. It's funny how software that was first used primarily as a goof-around, social tool has become a way for people to have business meetings and shop talk.

Other groups of people who IM, however, do it mostly for social reasons. These people are generally flagged "available," and they have vast contact lists that look more like a MySpace friend list than an office contact sheet. Occasionally, these social IM users and I have passed in the night, as it were: one of them will casually message me because they don't consider it weird to approach a stranger on IM to chat. For them, IM is like a giant nightclub or college campus.

Usually, my "away" flag wards these people off, but sometimes it doesn't, and I have to politely tell them I'm busy. And I frankly refuse to respond to a repeated "heya, wassup?" from anybody whose name is something like SFKitty233. Unless, of course, SFKitty233 happens to be my colleague. Which she just might be.

Annalee Newitz is a surly media nerd who is probably messaging somebody on IM right now.

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