Before participating in the Beta program, you should consider that as this is a pre-release service there may be occasional service interruptions and system downtime. This should be considered as a testing ground for you to explore the new features and functionality offered by the service.
To enable your Microsoft Office 365 tenant for BlackBerry service, you must log in to your office 365 account as an administrator an follow these steps:
On the Admin page, under Resources click on Setting up email on mobile phones
Under Set up BlackBerry Business Cloud Services click on Enable BlackBerry Business Cloud Services
Next step to activate the service is to authorize RIM to access your Office 365 account meaning that RIM will have Full Access to your Exchange Online information. If you are ok with that in the Beta program, confirm the the page.
Once you are done, you will be directed back to the Office 365 Admin page and you can see BlackBerry service is there under Authorized Services
If youclick on Manage, you will be redirected to BlackBerry Business Cloud Services for Microsoft Office 365 Provisioning page on BlackBerry's website which you can nominate your business for participation in Beta Program by visiting http://www.blackberry.com/beta/businesscloud
and clicking on Nominate an Organization on the right.