Stephen Elop just announced (at the Mobile World Mobile Conference in Barcelona) that Blackberries popular cross-platform mobile messenger app is coming to Windows phone "in the coming months".
BBM them sent a press release clarifying that BBM for Windows Phone will be available this summer. Additionally we learned that BBM will also be available for the new Nokia X Android phone also. The press release also confirms that all BBM 2 features will be available at launch (BBM channels, voice, video, etc).
BBM Press Release (link)