On IM, Keeping Tabs and Keeping Up Appearances

That roster, often called a buddy list, makes it possible to combine a person's personal, work and family lives from different eras and bring them all together on one screen.

The effect for those who see their buddies pop up unexpectedly can be like a single window across the street lighting up at 3 a.m. Or it might feel like having a continuous high school reunion with people showing up at random times.

In Muth's case, the buddy list functions like a tattered address book she has toted around since high school and includes names of friends who may almost never log on or with whom she's fallen completely out of touch.

It even includes a guy she dated and broke up with, on IM, three years ago. She hasn't spoken to him since, and on the rare occasion she sees his name pop up, he has usually posted a message recounting drunken escapades from the weekend before, she said. "Every time I see his stuff, it makes me very glad that never got anywhere."

Washington attorney Joel Bernstein can check in on his instant message system to see whether his 12-year-old daughter has logged on and is therefore home from school.

Clint Davis, 45, often scans his IM at work to see, at a glance, who's logged on and at work. "It's like attendance," the Internet content manager said.

Over time, companies such as Microsoft say they expect to pair location information with instant messaging, making it ever more possible for buddies to pinpoint a person's physical and technological accessibility. AOL LLC's AIM system, for example, already shows whether a person is logged onto instant message on a mobile device. Skype users with Web cameras can post icons to alert other users of their ability to video conference.

"People get to know one another's habits pretty quickly," said Naomi Baron, a linguistics professor at American University who has studied college students' uses of IM. Knowing that gives them a greater sense of control in relationships, she said.

But as technologies and users become more sophisticated in how they use IM, they devise more complex ways of revealing or masking their true availability.

"You can have an 'away' message up but still talk to people" online, said Kristin Washco, 16, explaining one of the paradoxes of online existence. "If I don't want to talk to someone, it looks like I'm away."

Often the high school junior, who uses AIM, will leave notes attached to her "away" status informing her 100 contacts that "I'm in a bad mood," or "I have a lot of homework" to explain her absence.

Washco is in the 58 percent of IM users who customize the messages they leave when they are away from IM, according to AOL, which surveyed some of its users in November. Twenty-five percent of those surveyed change their away messages daily, while 14 percent said they change them every time they are away from their computer.

The reverse is also true, said Washco -- away messaging can be used to beckon people into conversation. If a love interest is online, Washco and some of her girlfriends take down their away message in the hopes that their new available status will entice the person to send a message to them.

"You wait to see if they'll IM you," she said, in what is the rough equivalent of trying to walk by a guy you hope might ask you to the prom.

The move toward constant reachability through mobile phones, laptops and instant messages also creates a backlash among people who feel the need to shut down the chaos and withdraw from it.

All major IM software systems have features that allow a user to log on while remaining invisible to other users -- a phenomenon some call "lurking."

But using one's status as a ruse to hide comes with its own risk.

Washco said a classmate's attempt to hide her presence from another girl provoked a fight at school last year.

"You blocked me," the accuser said, according to Washco. The alleged blocker denied it but was caught in a lie; her accuser had multiple IM accounts and spied the girl logging on through one of those.