Customers everywhere would define "World Class Customer Service" differently. They may consider the representative's level of attentiveness, or the efficiency of the service. However, there are very specific guidelines that customer service organisations use to measure world class customer service. These guidelines are usually divided into three parts: greeting, research and action.
The Definition
According to Beldingskills.com, an organisation that specialises in customer service training, "World Class Customer Service, as we define it, is the process of consistently communicating to every customer--whether it is an internal customer or external customer--that they are valued, and that their satisfaction is paramount to your organisation."
Active Listening
Active listening is critical to determine the real reason that the customer is contacting you. There's nothing worse (for the representative or the customer than spending five minutes trying to resolve the wrong issue because of a communication error. The most effective tools to show that you are listening are open-ended questions and summary statements. "I'll be happy to change your address for you" would be a good summary statement. "So I can make sure you have everything you need, would you mind telling me a little about your situation?", would be considered a good open-ended question.
Action
After the customer service agent has convinced the caller of his sincerity, and done the research to determine all of the customer's needs, it's time for action. Depending on the situation, that might be resolving a problem, or providing education or clarification. It could also mean anticipating future needs and bringing those to the customer's attention. Regardless of what form it takes, the action is dependent on the first two phases being effective.