RIM's BlackBerry devices offer little value for most customers without being able to integrate smoothly with Exchange--Microsoft's messaging platform. As for Microsoft, it has to recognize that RIM's BlackBerry smartphones are a dominant force in mobile messaging, and make sure it is catering to that business audience. Microsoft also benefits by giving customers an additional reason to consider Office 365 over the rival Google Apps cloud-based productivity suite.
There is no set launch date at this point. RIM will conduct limited beta testing of the BlackBerry Office 365 service, with the intent of making it officially available later this year. It is expected that the service will launch in conjunction with the official launch of Office 365 by Microsoft. There is also no official date for that, but it is predicted to be sometime around June.