

A coworker of mine changed his voicemail message to start with the tri-tone that plays for a disconnected number (bah dah deet) followed by a normal voicemail greeting. The auto dialers delete the number from their list when they hear the tri-tone. It did confuse legitimate callers that were trying to reach him though.
We already have the precedent (see Andry José Hernández Romero, for example). Someone with power might be able to reverse it.