I worked customer service in a call center (aka the modern day salt mines) for ten years. All you say is true, but also please remember that those people wouldn't be calling if they didn't have a problem with the services your company provides. A calm, cool, professional and empathetic person on the other end of the line can do a lot to reforge a relationship with an unhappy customer.
Vent at them after they're off the phone, and be grateful you're not dealing with them in person.