While most marketing studies have focused on what salespeople say, less is known about the persuasiveness of how they say it, particularly in the distinct contexts of customer acquisition and retention. This research investigates how salespeople’s vocal brightness and loudness influence new and existing customers’ purchase behavior. Based on two studies conducted in China (a field study using a large real-world dataset of over 8,000 telephone calls and a randomized controlled experiment), the authors find that high brightness and high loudness positively predict new customers’ purchase behavior and timing, whereas low brightness and high loudness positively affect existing customers’ repurchase behavior and timing. The authors demonstrate that perceived arousal is the underlying mechanism driving customers’ purchase behavior in customer acquisition, while perceived competence serves as a mediator in customer retention. No effect of brightness or loudness on purchase volume is observed in either customer acquisition or retention. This research makes theoretical contributions to the marketing and nonverbal communication literature and provides valuable managerial insights regarding how to manipulate voice features to improve sales performance.