Lee is a commercial support customer and we helped him offlist with this. There was a problem with the siproxd package, it should now work. Lee confirmed he now has two phones working simultaneously, so this must be working now.
If you have installed the package previously, uninstall it first. Then replace /etc/inc/filter.inc with this one: http://cvstrac.pfsense.org/fileview?f=pfSense/etc/inc/filter.inc&v=1.1092 and reinstall the package. Then configure it, save your changes, and it should work. With it you should be able to connect multiple phones on one public IP. This is good news - one more limitation knocked out! Thanks to Lee for providing access to the system and testing our changes.
