As telephone scams become increasingly prevalent, it is crucial to understand what causes recipients to fall victim to these scams. Armed with this knowledge, effective countermeasures can be developed to challenge the key foundations of successful telephone phishing attacks. In this paper, we present the methodology, design, execution, results, and evaluation of an ethical telephone phishing scam. The study performed 10 telephone phishing experiments on 3,000 university participants without prior awareness over the course of a workweek. Overall, we were able to identify at least one key factor-spoofed Caller ID-that had a significant effect in tricking the victims into revealing their Social Security number.