I'm having trouble with getting the voicemail to work when an external caller is directed to an extension's voicemail. When making a call from one of our internal VOIP phones to one of our internal VOIP phones, the voicemail greeting is played and the caller can successfully record a message. However, when an external caller is directed to voicemail, no message is played and the line is absolutely silent. This means that the cannot save a recorded message. I've had a look at the firewall, and it doesn't look as though any sound is being rejected. The 3CX Activity Log doesn't give us any clue as to what might be going wrong. Is there a config setting I'm missing?