From the Exchange Team Blog:

Today Microsoft announced some significant changes to its licensing and support policies for applications in hardware virtualization environments. There are two key parts of the announcement worth highlighting for Exchange customers:

  1. Microsoft now supports Exchange Server 2007 SP1 running Hyper-V or hypervisors validated under the Microsoft Server Virtualization Validation Program (SVVP).
  2. Microsoft is waiving its 90-day license reassignment policy to enable customers who virtualize Exchange to move their licenses between servers within a data farm as often as necessary.

Microsoft Support Policies and Recommendations for Exchange Servers in Hardware Virtualization Environments is a must-read for anyone considering a virtualized Exchange environment.

To learn more about the Microsoft-wide changes to licensing and support, see: