Thanks for the replies.
I changed my sip.conf to below:
disallow=all
allow=g729
allow=ulaw
my conf. option is working fine, BUT my phone is not using g729 even for normal calls. by default it is going with ulaw codec. i dont have sufficient WAN bandwidth and that was the reason i purchased g729 licenses. Any help would be highly appreciated.
If some one has Cisco 7940/7960 with conference option enabled, please send me the phone setting (.cnf) file for me.
Thanks
Sekhar.