Hi aslam,
I understand from your description that you said PSTN calls which i think it is the local calls which you may mean that calls which pass through the PSTN
Are your mobile calls gateway is the same for PSTN [local ?] calls, if you have another gateway [like prima cell] then you should start thinking about it and about its voice ports
If you have a prima cell,it is normal to take some time [2 to 3 seconds] for the sim-card to call the needed mobile number, unlike the land line which call the local number immediatly
wish this be helpful
Thanks