I spent ages trying to figure out why our VoIP base station could not connect to the external PBX through Pfsense, only to find out that Pfsense works quite happily with VoIP with minimal configuration. The culprit was a setting on the router under the NAT section called “SIP ALG” – as soon as I disabled SIP ALG, everything worked perfectly. No NAT rules, or port forwarding in Pfsense required.