Hi Waleed,

Here is the info for building Unity with Failover;

About License Requirements for Failover

When Cisco Unity is configured for failover, the requirements for system keys or license files vary depending on the Cisco Unity version installed.

Cisco Unity Version 4.(x)

License files are installed only on the primary server. The Install License File wizard extracts the license data from the license files and stores the license data in the UnityDb database. When you run the failover configuration wizard on both the primary and the secondary server, the license data in the UnityDb database replicates to the secondary server. When this replication occurs, all of the features enabled on the primary server are enabled on the secondary server.

When you run the failover configuration wizard, it makes the license files available to the secondary server. If you do not run the failover configuration wizard on both servers, the secondary server cannot access the license files from the primary server and therefore is not enabled. Installing license files on the secondary server has no effect and does not enable any features.

Without contact with a primary server (and its license files), the secondary server will continue to function for a limited time.

From this good doc;

http://www.cisco.com/en/US/products/sw/voicesw/ps2237/products_white_paper09186a008019c743.shtml#wp1036734

Cisco Unity Failover Configuration and Administration Guide

http://www.cisco.com/en/US/products/sw/voicesw/ps2237/products_feature_guide_book09186a00801b9241.html

Hope this helps!

Rob