[SR-Users] Kamailio not responding

I have recently installed kamailio on CentOS 6.3 and configured a couple of SIP phone Linksys and Grandstream to test inercommunication. The SIP-Server/ Kamailio server ha started and is listen on port 5060. The UA are sending registered message to the SIP Server but there is no response from the SIP server. I left the syslog at default but not seeing any messages on the /var/log/messages. Can someone tell me if I have missed some configuration information. Note: I registered two users 101 and 202 using the command kamctl add 101 101. Is it possible to check whether the Users added have been added to the system??. and does anyone have any idea how to to troubleshoot a response from the Server. I am using Wireshark to monitor communication between between UA and SIP Server