Starting today, Blackberry services for BPOS users is now available for free.
For the coming Office 365 offer, this service will be also free BUT with some change.
Indeed, the Blackberry service, now called Blackberry Hosted, will directly hosted by RIM and now more managed though Office Online services.
Mode detail about this announcement here http://community.office365.com/enus/office365/b/microsoft_office_365_blog/archive/2011/03/16/office-365-and-blackberry.aspx