The initiative, which will take place over the coming months, means that users of Yahoo! and Microsoft's instant messenger services will be able to exchange messages, view other user profiles and add new contacts across the two company's instant messenger (IM) services for no extra cost.
The move was prompted by user requests for combining its IM services with Microsoft, said Brad Garlinghouse, senior vice-president of communications, community and front doors at Yahoo!.
Windows said combining the two IM services, which would create 350m registered users, and would allow users greater convenience, control and freedom in web communication.
Blake Irving, corporate vice-president of Windows Live Platform at Microsoft, added: "We're proud to deliver this latest advancement in IM services that empower people to communicate with virtually whoever they want, wherever they want and whenever they want."
The new interoperability trial will be available through the Yahoo! and the Microsoft across 19 international markets over the next few months.
The countries participating are: Argentina, Australia, Brazil, Canada, China, France, Germany, Hong Kong, India, Italy, South Korea, Mexico, Netherlands, Singapore, Spain, Taiwan, Turkey, the UK and the US.
Yahoo! and Microsoft have not said how long the trial will last.
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