After announcing that BlackBerry service for Office 365 was in beta, it seems the service is now live since few days (see http://blog.hametbenoit.info/Lists/Posts/Post.aspx?ID=297) but still in beta. The program is currently accepting new participant. To take part of it, go to https://www.blackberry.com/beta/businesscloud
If you connect to your Office 365 administration portal (https://portal.microsoftonline.com) as administrator and go to Setting up email on mobile phones below the Resources section on the right
You will have the possibility to activate BlackBerry Business Cloud Services.
When you activate the service, you have to accept BlackBerry Business Cloud Services to access your Office 365 tenant. This means RIM will have full access to your Exchange Online data (more details here http://g.microsoftonline.com/0BX10en/278)
Once the service has been activated, a new section appears at the end of the main administration page, called Authorized Services where you will be able to manage additional services authorized to access your tenant; in this case, BlackBerry Business Cloud Services.
If you click on the Manage link, you are redirected to a BlackBerry web site where you will be able to manage your BlackBerry users.