Hi Pushpak,

Here are some good threads that speak to this issue, and detail some 3rd party products that can get this info. I have known people that include the Serial # in the phone description (via handheld scanner) so they can get at this info easily later on.

http://forum.cisco.com/eforum/servlet/NetProf?page=netprof&forum=Unified%20Communications%20and%20Video&topic=General&CommCmd=MB%3Fcmd%3Dpass_through%26location%3Doutline%40%5E1%40%40.1dd8ce53/1#selected_message

http://forum.cisco.com/eforum/servlet/NetProf?page=netprof&forum=Network%20Infrastructure&topic=Network%20Management&CommCmd=MB%3Fcmd%3Dpass_through%26location%3Doutline%40%5E1%40%40.1ddcf30e/0#selected_message

http://forum.cisco.com/eforum/servlet/NetProf?page=netprof&forum=Unified%20Communications%20and%20Video&topic=IP%20Phone%20Services%20for%20End%20Users&CommCmd=MB%3Fcmd%3Dpass_through%26location%3Doutline%40%5E1%40%40.eea4a36/1#selected_message

http://forum.cisco.com/eforum/servlet/NetProf?page=netprof&forum=Unified%20Communications%20and%20Video&topic=IP%20Telephony&topicID=.ee6c829&CommCmd=MB?cmd=pass_through&location=outline@^1@@.2cc0e75f/1#selected_message

http://forum.cisco.com/eforum/servlet/NetProf?page=netprof&forum=Unified%20Communications%20and%20Video&topic=IP%20Telephony&topicID=.ee6c829&CommCmd=MB%3Fcmd%3Dpass_through%26location%3Doutline%40%5E1%40%40.2cc1b411/1#selected_message

Hope this helps!

Rob