Users of IBM's Lotus Sametime instant-messaging service will be able to connect to people on the rival AOL and Yahoo networks under a deal that underscores the technology's transformation from a program for chatty teenagers into a common business tool.

The arrangement announced Monday by International Business Machines Corp. means that the 15 million people who use Sametime on the job also will be able to communicate with customers, friends and relatives who "IM" on the popular consumer-focused networks run by Time Warner Inc.'s America Online and Yahoo Inc.

Separately, IBM and Google Inc. are in discussions toward linking Sametime with the new Google Talk IM service.

Instant messaging grew up in distinct silos — each service let users chat and set up "buddy lists" with just its own members. Users clamored for "interoperability," but the companies behind the services were reluctant to give up a hold on their user bases.

Little by little, the walls surrounding the IM networks have come down. The biggest such breakthrough came in October, when Microsoft Corp. and Yahoo agreed to make their widely used instant messaging programs for general consumers work together by June 2006.

Even before that, though, free "bridging" services linking multiple IM networks arose, such as Trillian. And several smaller IM networks in the business world are linked with other services. In fact, AOL said that with the Sametime deal, its networks will be linked to more than 75 percent of business IM users.

The big player on the sidelines here is Microsoft, which has its own product, Live Communications Server, that lets business users send and receive messages from the Yahoo, AOL and MSN systems.

While IM has become an easy way for people in business to connect to colleagues and customers, concerns have arisen about the security of the public networks, which can be vulnerable to worms and other attacks.

Because Sametime is aimed at the corporate market, IBM contends it can assure its security and integration with companies' networks. Big Blue hopes that linking to the consumer IM networks takes away the downside that Sametime users essentially can talk only to each other.

When this new, interoperable version of Sametime debuts in the middle of the year, IBM will add some flourishes that have long existed in the consumer market, including video and voice connectivity.

Sametime also will get the ultimate staple of regular-Joe instant messaging: the ability to send happy, sad, winking or angry faces known as "emoticons."