DIR-655 Vonage in DMZ

I have vonage hooked to one of the LAN ports on my DIR-655 I also have the vonage adapter in the DMZ. When making or receiving calls every few seconds I get a drop in audio. I called Vonage tech support and they told me to use port forwarding. If a device(vonage) is in the DMZ dosen't that mean that everything passes through it regardless if port forwarding is on or off?

Anyway, Sharepoint is off QOS is still on. Vonage has a static IP address but I am still getting this problem. I am not sure what to do. I may just have to give up on vonage.

Thanks