Occasionally during a phone call one user will lose the audio stream. So that user will suddenly say 'Can you hear me?' and the other user will reply 'Yes', but the first user cannot hear them. Typically the call is terminated and restarted and we scratch our heads. We have tested with a different handset, and a hard-wired phone and the problem does not seem to be the phone per se, but at or beyond the ATA. Any troubleshooting suggestions or ideas?