Unless you have a bad VOIP card on the NEC I seriously doubt the NEC is the issue unless something is really programmed wrong. All the codecs need to be in line. SIP ALG needs to be off. I am assuming you are not using a session border control unit. SIP ALG needs to be off on the router/firewall. Codecs must match that's one issue to be sure. Carriers like to compress but sound quality sucks on anything less than 7.11. With so little traffic something basic is going on. I have hundreds of NEC units in the field and I have never seen it an issue with NEC like ever. Seriously consider replacing the PFSense with a different router. ANY router like an ASUS WRT or whatever and see if it goes away. Ya I would simplify the networking and work from there because with that little network, unless you have some real bad latency issues...shouldn't be an issue. Are you running the computers through the phones?

Coral Tech
www.pantelonline.com