At the time of the announcement, RIM's senior vice president for the BlackBerry platform Alan Brenner said "The BlackBerry developer community has been eagerly awaiting the opportunity to integrate BlackBerry Messenger with their apps. BBM is a very popular service with over 28 million users and opening its real-time social connectivity to third party applications presents incredible opportunities."
He added "Access to BBM services from within apps will revolutionise gaming, enhance multimedia experiences, and add a new dimension to location based applications."
BBM now has more than 35 million active users.
The beta release gives developers access to the API and simulators for BlackBerry OS 5.0 and 6.0. The next step, scheduled for next month, will be the addition of full support for BlackBerry WebWorks (RIM's platform for developing BlackBerry apps in Eclipse or Visual Studio).
The SSM SDK and other details are available via this page.