Recording for voicemail systems

I recently had to pass on a voicemail VO project. I couldn’t get the quality that the
client wanted either in 8 or 16-bit mono. Is there a “best” audio file format setting for voicemail recordings?
If so, are the settings settable on Audacity 1.2.6? Thanks for responding!


Ummmm. What? What’s a voicemail voice over?

Music CD sound is 16-bit, so something else was going on.