You have a very distinctive voice - warm, deep and clear. In fact, it is so beautiful that I'm surprised you're not doing radio or commercial voice overs. You should look into that.
So when your automatic dialing device called this same number and you asked for my other boss, the one whose first name starts later in the alphabet, I recognized it right away.
Dear Person calling Other Boss:
When I say he's not available, that means he isn't and no amount of telling me that you need to talk to him will change that. And if voice mail is acceptable at the end, why is it not acceptable at the beginning?