Office 365 supports BlackBerry operating systems 4.2, 4.3, 4.5, and 5.0, and Microsoft plans to support future releases. As of this writing, BlackBerry Enterprise Services (BES) services offered by RIM are not available in Plan P1. BlackBerry users can use BlackBerry Internet Service (BIS) to connect to Office 365. The difference between BES and BIS is that with BIS you are essentially accessing Outlook Web App (OWA) in your mobile browser. That’s quite a bit different from having a mailbox client on your phone. The BES experience is preferred but, as mentioned, is available only in the Office 365 E plans. You can find more information about BlackBerry Cloud Services at http://docs.blackberry.com/en/admin/subcategories/?userType=2&category=BlackBerry+Business+Cloud+Services.