Hi Muzzamil,
What version of Call Manager are you running? This should be supported as of Version 5.
The following link explains configuring a Cisco IP handset to use SIP:
http://www.cisco.com/en/US/products/hw/phones/ps379/products_tech_note09186a0080094584.shtml#topic1
If you are seeing the registration rejected message on the phone, it could be that you have either not added the device to Clall Manager or you have not enble auto registration on the Call Manager cluster.
I would also have a look at this document to check the auto registraion:
http://www.cisco.com/en/US/products/sw/voicesw/ps556/products_tech_note09186a0080708526.shtml
If you are not configured for auto registration, you will need to manually add the device by entering it's MAC address in Call Manager.
Post back if this helps or not, and good luck!
Kind regards, Ash.
