I know that even voice response systems that are not state of the art can tell you, the phone answerer, how long I've been waiting. So in the interest of treating both of us as human beings, I think it would be useful to say something like, "Sorry for making you wait eleven minutes, how can I help you today?" People who react belligerently to that will do so to anything, so there's no helping them. We don't all have to be cogs.