Ha, nice. My wife's trick is to make it as non-personal as possible. "I know it's not your fault, but <insert problem>. I'm not mad at you, but you might understand my frustration at <restate problem>.". Also - stay on the line as long as it takes...most of them are measured on how fast their turnaround is and they're not allowed to directly hang up on you (as long as you're not being hostile or overly rude), so eventually they'll do whatever it takes to get you off the phone.
Right, the non-personal thing is key. They just answer the phones all day and try to make up for other people's mistakes. Most of them are sensitive to your problem, they just don't want to be unfairly treated as if they were the root of it.
