Hey Craigduff, thanks for your reply!
The pfsense version that I have been using is from the 2.1 dev branch
(specifically 2.1-DEVELOPMENT (i386) built on Sun Sep 11 21:36:53 EDT 2011
FreeBSD firebox1.virtualflo.com 8.1-RELEASE-p4 FreeBSD 8.1-RELEASE-p4 #1: Sun Sep 11 21:36:18 EDT 2011 root@FreeBSD_8.0_pfSense_2.0-snaps.pfsense.org:/usr/obj./usr/pfSensesrc/src/sys/pfSense_SMP.8 i386)
This is the same version that I have been using since mid-september and the same version under which this configuration worked just fine.
The phones can call each other internally without issue.
For some reason, the forwarded sip port appears closed from outside.
In the firewall logs I can see that the device is talking with servers outside the lan.
There is quite a lot of chatter going from lan -> wan, but no traffic going from wan -> lan at all.
Example, making a call to my mobile phone:
Mar 27 11:58:47 LAN 192.168.1.30:5004 126.96.36.199:21162 UDP
Mar 27 11:58:21 LAN 192.168.1.30:60279 188.8.131.52:80 TCP:S
Mar 27 11:58:18 LAN 192.168.1.30:60278 184.108.40.206:80 TCP:S
Mar 27 11:58:15 LAN 192.168.1.30:32978 220.127.116.11:53 UDP
Mar 27 11:58:11 LAN 192.168.1.30:60277 18.104.22.168:80 TCP:S
This results in one-way audio. I can hear sound on the mobile phone, but on the handset there is no sound.
Hanging up on the mobile phone causes the handset to think that the connection is still live.
Calling from mobile to the sip line results in a 'this number is not available' message.