While many organizations are interested in having an Address List Segregation solution, they should clearly understand that this is not a commercial solution and Microsoft Hosted Messaging and Collaboration Solution (aka HMC) stands as the commercial solution. The last version currently available for HMC is 4.5 and hosting in Microsoft Exchange Server 2010 will be available approximately "Exchange Server 2010 release date plus twelve months". Microsoft will support HMC 3.5 through July 12 2011, and will support HMC 4.x through December 12, 2011.
Support for ‘Address List Segregation’ Solution should also be understood clearly and Dave wrote in his blog on this topic last month. This blog can be read at http://blogs.msdn.com/b/dgoldman/archive/2010/05/10/critical-update-exchange-2010-address-list-segregation-and-current-support-stances.aspx