A few years ago, ICQ and AIM joined forces and opened their network to communicate to eachother.
A few days ago, MSN opened their Network to the Yahoo Network.
“This first-of-its-kind interoperability between consumer IM leadersMicrosoft and Yahoo! gives our customers tremendous control,convenience and freedom in their Web communication experiences withWindows Live,” said Blake Irving, corporate vice president, WindowsLive Platform at Microsoft. “We’re proud to deliver this latestadvancement in IM services that empower people to communicate withvirtually whomever they want, wherever they want and whenever theywant.”
Windows Live Messenger and Yahoo! Messenger with Voice users in theU.S. and more than 15 international markets can register to participatein the IM interoperability beta by visiting Yahoo!.The new beta program will be available in Argentina, Australia, Brazil,Canada (English and French), China, France, Germany, Hong Kong, India,Italy, Korea, Mexico, Netherlands, Singapore, Spain, Taiwan, Turkey,the United Kingdom and the United States (English and Spanish).
Personally I am not a fan of Microsoft nor Yahoo Messenger. The solution is Jabber! OpenSource and free! There are alot of Transports which give the user the possibility to connect to other Messenger Networks.
Flosoft Messenger, a Jabber Service, can be found at: http://im.flosoft.biz