Remove automatic line. Verify your trunk groups. By default its dial 9 access. Wire shark it cause something simple is being missed here.
I'll try that. I also agree that there has to be something simple and obvious that's getting overlooked. I may head into the shop tomorrow to frown at this some more -- I'm very motivated to solve this.
As for wireshark, we've been running tcpdump against the interface from the router that the SV8100 is physically connected to, so we're reasonably confident of the IP behavior. That said, I will absolutely go ahead and hook the system into a switch, span the port, and then use wireshark to make sure I'm not losing packets in the kernel or some other silliness on the router. It wouldn't be the first time I'd been bitten by something obscure.
