The very nature of hosted environment (Exchange, SharePoint, OCS, etc.) implies that the infrastructure or user base is partially or fully hosted and managed by Microsoft or one of the partners. For instance with BPOS, you have a choice between Standard and Dedicated Versions. The former supports multiple customers with a single architecture (5 seat minimum) whereas the latter uses one architecture for each customer.
More info and sign up for a trial or subscription at
https://mocp.microsoftonline.com.
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