The total minutes U.S. workers spent using the top three instant-messaging applications--from America Online, MSN, and Yahoo--increased 110%, from 2.3 billion minutes in September 2000 to 4.9 billion in September 2001. The number of unique users of instant-messaging applications in the workplace also jumped 34%, from 10 million in September 2000 to 13.4 million in September 2001.

While AOL has the most users in the workplace, MSN and Yahoo are quickly gaining in popularity. In some cases, employees are using more than one brand of messenger. The Jupiter report indicates that 23% of workers with IM use at least two competing brands, compared with 18% in September 2000. Users are finding ways to directly communicate with people on different instant-messaging networks, Jupiter adds.

AOL, the IM market-share leader, is working toward IM interoperability with Lotus and Sun Microsystems, but no clear standard has been developed yet. MSN is also reportedly collaborating with British wireless carrier Genie to let European cell-phone users communicate with MSN messenger users from the Genie IM service installed on their phones.