Voicemail is always a carrier issue. How can calls with no message be saved? Unless the caller stays on the line long enough for the greeting to complete, there would be nothing to record. If the caller stays on, the vmbox will hear the sound of the disconnect and record it. If the caller hangs up before the greeting is complete, there will be no "blank" message saved. No one can prevent a spammer from leaving a message, so they will always be recorded, just as any other message.
