Please make sure that SIP ALG (Application Layer Gateway) as well as any DPI (Deep Packet Inspection) is disabled on all of your network equipment including your ISP modem.
If your router supports QOS, configure QOS rules on your router / firewall to prioritize the traffic on these port ranges so the voice traffic is processed ahead of the data traffic: 5060-6000 UDP –AND- TCP 16384-16482 UDP 20000-60000 UDP
Either I'm impatient, blind, or Comcast is loaning subpar equipment to businesses.
Need to configure the router side of the modem/router device. Router lacks options/features. Business has VoIP services for a call center and call center is always having issues. Per provider of VoIP, instructions ask me to configure three items, all of which these routers lack and may in fact be causing trouble with our VoIP services.