Running FW 2.1.5 and when calling inbound over SIP trunk and call is transferred to VM, the greeting played is garbled. Issue also with FW 2.1.4.
A similar issue exists per post https://supportforums.cisco.com/thread/2128159 however NAT Keepalive has been since turned off and still running into the issue.
Internally when dialing voicemail the greetings played is very clear and the issue is only when calling over SIP trunk. Codec is set to G711u.