Instant messaging users have been hoping for covergence among the various systems for quite some time, but companies have thus far been reluctant to provide it, since they're competing to build their user bases. But convergence came a step closer Monday, when IBM (NYSE:IBM) announced an alliance that will let its Sametime corporate messaging program communicate with IM programs from several industry heavyweights.

On first glance, the agreement's biggest surprise was the presence of Time Warner's (NYSE:TWX) AOL and its industry-leading AIM service, which has stubbornly kept mostly to itself. Yahoo! (NASDAQ:YHOO) Messenger will also be able to connect with Sametime, and Google (NASDAQ:GOOG) is also in talks to do so.

Yahoo! has shown willingness to play ball in IM before; you might recall that not too long ago, it announced a hookup with Microsoft's (NASDAQ:MSFT) instant messaging program, which seemed smart considering the lead that AIM has on both of them. Google's no surprise either; there have been hints that Google Talk might one day bring interoperability between the different services to the table, which would make its version more competitive. Without that feature, it drags along behind. (When my Foolish colleague Seth Jayson wrote about the launch of Google Talk, he described using the service as "showing up early at a cocktail party" -- this remains the case.)

Then again, despite its might, maybe it's not such a surprise that AOL would hook its IM services up with Sametime. According to AOL's press announcement on the subject, the agreement exposes AIM to a total 75% of corporate IM users. AOL's AIM, ICQ, and Apple (NASDAQ:AAPL) iChat users will all be able to connect with Sametime users.

And while AIM boasts 40 million users in the U.S. alone, IBM's Sametime instant messaging system has 20 million users in the coveted business demographic; IBM claims that 60% of the world's largest companies use its system. Microsoft may have a mere 15 million users for its MSN Messenger program, but it also has a messaging platform for business, Live Communications Server, which likely explains its reticence in hooking up with Sametime.

The corporate market has long been a holy grail for the IM services. Now, with all the big players adding VoIP, videoconferencing, and other whizbang features, it stands to reason that IMs will play an ever-larger role in everyday communication -- especially in the workplace. If the Sametime agreement is any indication, too much isolationism is no way for any IM service to win.

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Time Warner is a Motley Fool Stock Advisor selection, while Microsoft is a Motley Fool Inside Value pick. We've got more great newsletters chock-full of Foolish insight, and you can try them free for 30 days.

Alyce Lomax does not own shares of any of the companies mentioned.