I have a trixbox server and every works find except the external SIPs. Inside net all sound goes fine, but if I use a SIP phone outside the net, I can connect, I can receive calls but I there is no sound.
I have this text in the sip_nat.conf:
nat=yes externhost=xxxxx.dyndns.org localnet=192.168.1.0/255.255.255.0 localhost=192.168.1.210 externrefresh=10 qualify=yes
And I have the ports from 5036 to 5082, 4569 and from 10000 to 20000 redirected to 192.168.1.210 on TCP and UDP.