There is no audio when a user dials to the VOIP number of the PBX. The user in the extension can hear the other user on the phone, but the user on the phone is unable to hear back from the user using the extension. But when the user using the extension dials outside to land line, the audio is two way and is clear.
I have tried assigning public address with NAT for the VOIP server, disabling Windows firewall, unblocking all ports and also tried options stated in http://www.nch.com.au/pbx/kb/99.html. Please suggest.