Instant messaging isn't just kid stuff anymore.

IM, often dismissed as a medium for teenage socializing and homework avoidance, has skyrocketed as a workplace phenomenon in the U.S. over the past year, according to research released Wednesday by Jupiter Media Metrix.

In September 2001, the total number of workplace minutes spent using the top three IM applications amounted to 4.9 billion, more than double the 2.3 billion minutes of workplace usage that Jupiter Media Metrix calculated for 2000.

The number of workers using at least one of these three IM programs -- specifically,

AOL Time Warner's

(AOL)

AOL Instant Messenger and ICQ,

Yahoo!'s

(YHOO)

Yahoo! Messenger and

Microsoft's

(MSFT) - Get Report

MSN Messenger -- has grown to 13.4 million from 10 million a year earlier.

IM usage at home continues to overshadow workplace usage, though the number of home-based IM users has been growing at a slower pace. The total minutes using IM in the home grew 48% from a year ago, according to Jupiter Media Metrix, amounting to 13.6 billion in September 2001. The total number of home-based IM users grew 28% in the same period, to 53.8 million.

IM's growth in the workplace is significant, because AOL, Microsoft and Yahoo! are pitching it to the enterprise market as a productivity tool rather than the time-wasting diversion that employers often perceive it to be.

The ability of IM users to communicate from remote locations with almost instantaneous feedback was spotlighted soon after the terrorist attacks of Sept. 11, when computer users, connected to the Internet via local dial-up connections, were able to communicate with distant friends, families and colleagues despite jammed long-distance phone lines.

For Yahoo!, Microsoft and AOL, instant messaging represents a tremendous opportunity to reap new revenue and drive usage of their other services. Each is encouraging users to use IM not only for typewritten chat, but also for receiving news alerts, travel advisories, stock-market data and other timely information. AOL Time Warner's reluctance to allow its AOL Instant Messenger application to mesh with other IM systems was

a lightning rod for criticism during the approval process for the merger that created the company.

According to the survey, AOL Instant Messenger continues to be the leading IM application at home and at work, though MSN Messenger and Yahoo! Messenger are picking up new users at a faster pace than AOL. The number of people using more than one brand of IM application is growing; at work, 23% of IM aficionados use at least two IM programs.