Hi Palanivel,
The requirements are listed in the doc below;
Requirements
Revised April 2, 2009
With the requirements listed below, Cisco supports virtualizing the following servers running the Cisco-provided software: Cisco Unity application servers, Cisco Unity voice-recognition servers, and Voice Mail Run-Time Edition of Microsoft Exchange Server 2003 servers (with or without Active Directory installed).
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Note This guide collectively refers to the three types of virtualized servers mentioned above as "Cisco Unity virtual machines."
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â¢Cisco Unity version 7.0(2) or later.
â¢VMware ESX 3.5 or later, or VMware ESXi 3.5 or later.
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Note This guide refers to both VMware ESX and VMware ESXi as VMware ESX.
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â¢VMware ESX must be deployed in a configuration supported by VMware.
Virtualizing Cisco Unity Messaging on VMware ESX
http://www.cisco.com/en/US/docs/voice_ip_comm/unity/virtualization_design/guide/cuvirtualdg010.html
Hope this helps!
Rob