Question: How do I perform a diagnostic on the audio?
Answer:

An audio diagnostic can be performed by selecting [MENU]→[Settings]→[Maintenance] →[Factory Functions] →[Audio Loopback], press Start to start the diagnostic test. Talk into the handset or the on-hook phone. If you can clearly hear your own voice, the audio capability on the GXV3140 is fully-functional. Press MENU or F4 to stop the audio diagnostic process.