configure cp960 on Vertical Wave Server

[lindale]

I have 2 cp960 conference phones provisioned on a Vertical Wave ip2500 phone system as 3rd party sip phones. I can get the phones to work but inbound audio whether outside trunk call or internal intercom or voicemail calls always deteriorate approximately 5 seconds into the call to where inbound audio is impossible to understand. Some times is clears up for a short time and then degrades again. I have worked with the vendor support and the captured audio is perfect from the wave server to the cp960, no degradation. I have called and left a voicemail with Yealink support but have never heard back. This phone does the same on our in house wave server, but works properly on a zultys mx phone system.