Currently (6.3 code) we do not support NAT'ing for Voice ALGs
If the ACL for the specific user-role has source NAT option enabled; we suggest in removing it since this is an unsupported configuration.
Voice ALGs do not support NAT. This is due to the way NAT functions and the way IP addresses are embedded in the signalling messages.
In typical customer's deployments, voice communications are confined within the internal network; thus doing away with the need for NAT.