As anticipated, Microsoft and Yahoo Wednesday evening launched a beta test of their instant messaging services to let their users to IM each other and add contacts from either service, reports Market Watch. Interoperability is the most-requested IM feature, according to a Yahoo spokesperson, who said more users will be able to join the test in the coming months.

Windows Live Messenger (the next generation of MSN Messenger) and Yahoo Messenger with Voice will now connect with each other, creating a global community of some 350 million accounts, writes CNET. The beta is being launched worldwide, in 15 languages.

The move is a challenge to instant-messaging leader AOL Instant Messenger, which alone accounts for nearly as many users as MSN/Windows Messenger and Yahoo Messenger combined. Moreover, Google and AOL are working to make their IM services interoperable, after Google invested $1 billion for a 5 percent stake in AOL.

In their announcement, the companies sad the 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).