Mutual scratching of backs could boost both firms.
BlackBerry Messenger, the once massively popular messaging app from the Canadian handset maker, is now available in beta on the Windows Phone store.
BlackBerry said that the app is "currently at capacity for the beta and will be working through our waitlist." However, the app should be released to the public once initial testing is completed.
Last year, BBM was released for Android and iOS, and now has millions of downloads on both platforms. Key features have been released for the app including video calling, voice calling, and regular updates that keep the app level with the messaging competition.
Last year, BlackBerry Software Product Management VP Andrew Bocking said: "For BlackBerry, messaging and collaboration are inseparable from the mobile experience, and the time is definitely right for BBM to become a multi-platform mobile service. BBM has always been one of the most engaging services for BlackBerry customers, enabling them to easily connect while maintaining a valued level of personal privacy."
The move benefits both Windows Phone, which struggles to attract developers from making popular apps for the operating system, and BlackBerry, which is struggling to profit from BBM.