Poly CCX phones are not fully compliant for use of the Opus codec with sip.audio

When using Opus, the payload type is fixed at 121, whereas sip.audio servers use the specified dynamic payload type for Opus. As a result of the mismatch, audio streaming fails.

ENABLING STUN

To enable and configure the phone to use the sip.audio STUN server, edit the phone's config file to include the following...

feature.nat.stun.enabled="1"
nat.stun.server="stun.sip.audio"