Hi, I'm having a problem with receiving calls. I am using a Polycom VVX500 I've set up manually with the service. I can place outbound calls without any trouble.

However, when I try to place an inbound call the VVX doesn't ring. If I plug it directly into my modem (so it isn't behind NAT) it does ring when I call. I would just use this solution, except I need to connect several of these phones in the same office.

Here's a little bit of info about my setup:

1) I have a Zyxel firewall as my main border router. I have UPnP enabled and SIP ALG disabled (I've read turning it on can cause problems).

2) I have tried this using a different phone, as well as a softphone and I'm getting the same problem.

Is there some special kind of port forward I need to set up or something? Any help would be greatly appreciated.