After years of mutually beneficial barriers between their respective networks, instant messaging's "Big Three" will finally interoperate, at least between enterprise users. An agreement between Yahoo, AOL, and Microsoft is aimed at IM customers looking for a way to provide chat between employees on different networks.

Microsoft announced early today that users of Microsoft's Office Live Communications Server (LCS) 2005 will be able to connect with AOL, MSN and Yahoo networks, providing the capability to share presence and, eventually, directory information between the three for enterprise users. The announcement comes less than a month after both AOL and Yahoo announced significant scalebacks in their enterprise presences and largely explains the value Yahoo saw in changing its IM protocols to block third-party clients. The deal is driven, according to some published reports, by Microsoft sharing revenue from the additional licensing fees it will collect for the capability to interoperate with the other two companies.

Statements from representatives of the three companies signalled that, while something of a breakthrough in terms of scope, the deal is less of an exclusive coup for Microsoft than it is the logical extension of AOL and Yahoo's desires to figure out a way to earn revenue from their IM networks. Less-major players have made similar deals with one or the other of the three companies, including IBM, which has agreements with AOL that allow its Lotus Instant Messaging customers to connect with AOL users outside the company network.