NAT Setup - No inbound calls

[StanAccy]

Im looking for things to check with regards to my NAT/Cisco 7960 setup:

Im running a Cisco 7960G (firmware 8.12) behind a Netgear router. I can make outbound calls fine. However, I have no inbound calls (phone does not ring).
Ive set the phone to use UDP port 5060 for SIP and 16384-32768 for RTP (all UDP).
Ive opened these ports on my firewall and sent all traffic on those ports to the static IP that my phone has on the LAN side.

Looking at my devices page on the voipo site, I see that I have three devices listed - 2 are the Grandstream device, and 1 is the Cisco 7960. However, for the Cisco I see empty entries for "Received" and "Connected To" (unlike the two Grandstream entries which have values set for these fields).

Ive set the following values in my SIPDefault.cnf file:

# NAT/Firewall Traversal
nat_enable: 1; 0-Disabled (default), 1-Enabled
nat_address: "mydomainname.com"; WAN IP address of NAT box (dotted IP or DNS A record only)
voip_control_port: 5060; UDP port used for SIP messages (default - 5060)
start_media_port: 16384; Start RTP range for media (default - 16384)
end_media_port: 32766; End RTP range for media (default - 32766)
nat_received_processing: 1; 0-Disabled (default), 1-Enabled

Any ideas on things to check for the inbound call problems?

Diagnostics dump from phone:

SIP Phone> sh register

LINE REGISTRATION TABLE
Proxy Registration: ENABLED, state: REGISTERED
line APR state timer expires proxyort
---- --- ------------- ---------- ---------- ----------------------------
1 111 REGISTERED 3595 3564 sip.voipwelcome.com:5060
2 111 REGISTERED 3595 3564 sip.voipwelcome.com:5060
3 ... NONE 0 0 undefined:0
4 ... NONE 0 0 undefined:0
5 ... NONE 0 0 undefined:0
6 ... NONE 0 0 undefined:0
1-BU .1x IDLE 0 0 undefined:0

Note: APR is Authenticated, Provisioned, Registered

So it looks like the phone is connected and authenticated - this leads me to believe its some sort of firewall / port routing issue but Im at a loss as to what to try next.