Can I use SIP if my PBX is behind a NAT firewall? June 24, 2010/in FAQs /by Brendan PolkYes, using SIP registration, this is possible. https://www.inflowcomm.com/logo/inflow_logo.png 0 0 Brendan Polk https://www.inflowcomm.com/logo/inflow_logo.png Brendan Polk2010-06-24 08:30:402016-07-05 04:15:30Can I use SIP if my PBX is behind a NAT firewall?