Instant Messaging (or IM) is the ability to easily see whether those in your "buddy list" are connected to the internet and, if so, to exchange messages with them. It's faster than e-mail, and less intrusive than a phone call.
But it entails some risks, particularly for businesses, where plain-vanilla IM is seen as providing an unsecured opening to the internet for virus infection, the leaking of confidential information and liability for defamation.
Microsoft, AOL and Yahoo! all offer corporate IM packages, with appropriate security additions, including means of recording the messages; but the lack of interoperability has hindered their success. Accordingly, the agreement now reached among the three biggest players may breathe new life into enterprise IM.