[dumpsterdiver]

Regarding the "fatal flaws" in such a system, the same could be said if someone were to strike up a conversation in-person.

If others see that a person is engaged in conversation, they might not be so quick to interrupt (that could come off as rude, and lessen your chances of success).

On the other hand, perhaps you are daring, and when you notice the person who is being DoS'ed frown when they answer the phone, you decide to stand up and actually say hello (effectively rescuing them from their attacker).