I already blogged earlier about the multi-tenant hosting possibilities in Exchange 2010 SP1 when using the /hosting switch during installation. This provides a true multi-tenant Exchange 2010 environment but lacks quite an amount of functionality, like Public Folders, the Unified Messaging Role, Lync Server 2010 multi-tenant integration (although an update on this is expected later this year) and provisioning difficulties. You can read my two earliers blog post on Exchange 2010 hoster edition and Exchange 2010 SP1 hosting & Control Panel. Although it is doable, it is difficult at the same time.
With the upcoming Service Pack 2 for Exchange 2010 there’s nothing new with respect to the Hoster Edition, but for a normal installation (also referred to as on-premises installation) a new feature called Address Book Policies (ABP) will be presented. The new ABP feature is the successor of the Exchange 2007 Address List Segregation (which is not supported in Exchange 2010 since it might horribly break Exchange 2010). This makes it easier for non hosting customers to implement multiple address lists without using the /hosting switch (please remember you need to be a registered hoster to officially use the hoster edition of Exchange 2010 SP1).