I moved the Vonage ATA to the outside of my firewall. I gave the ATA it's own public static ip address. When I did this, everything works fine. I think that there is some other port that needs to be opened for incoming connections, that is not specified in this document.
The only concern about putting the ATA outside of the firewall, is that I can not prioritize packets going to the ATA over others going to the rest of my network.
I have decided to try Speakeasy's VoIP. With Speakeasy VoIP Speakeasy, my ISP, can prioritize the packets to ensure high voice quality. The new adapter should arrive within a week, and I will try it then.
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