I won't go so far as to call this unethical, but this is basic social engineering. You're tricking somebody into violating the normal "flow" of external communications into the company. This may end up hurting that person if, say, they are identified as the reason that some random person schmoozed their way onto the phone with a busy higher-up.
Great post. I'm definitely going to have to go back and read your archive of sales advice.