Thanks pythonpoole, i've double checked the issue, Using Axon We can make internal/network calls ok,
we can call pstn & other SIP phone No's ok, but if someone calls us we can hear them but they cant
hear us.
Here's the NB6 settings i had:
type . external port . IP Address(of server) . internal port
tcp/udp . 5060 . 192.168.x.xx . 5060
tcp/udp . 8000-8025 . 192.168.x.xx . 8000-8025
Axon Settings:
General Tab:
Service Settings: Run on local service (no network access) ....... What does this mean?
Network tab:
Listening local port
SIP port: 5060
RTP port: 8000 (starting from)
Allow incoming calls:
ticked: use uPNP
ticked: Use STUN server
ticked: use static IP Address (public IP: xxx.xxx.xxx.xxx, external SIP: 5060, external RTP: 8000 (starting from))
Do these settings look ok? Let me know what u think 
Jim