In the dynamic telecommunications market of Indonesia, quality customer service is pivotal for sustaining competitive advantage. IOH faces persistent challenges in meeting customer service expectations, evidenced by consistent customer complaints regarding the customer service representative performance despite extensive training programs for their representatives. This study aims to evaluate the effectiveness of IOH’s customer service training programs in Jakarta, identifying key factors influencing training effectiveness and proposing improvements. Utilizing a quantitative approach, a survey was conducted among 49 customer service representatives, and the data were analyzed using spearman rank correlation. The results revealed that training content, method, schedule, and facilities significantly impact training effectiveness, with training content identified as the most influential. Improved training content to be more relevant with the needs of representatives, implement the diverse and interactive methods, well-structured schedules, and utilize the high-quality facilities can enhance the effectiveness of training programs. These strategies will enhance the competency and confidence of customer service representatives, ultimately improving customer satisfaction. Future research should explore personalized training approaches tailored to individual needs and assess the long-term impacts of training programs and expanding the study beyond Jakarta will provide a more comprehensive understanding of training effectiveness across different regions. By addressing these recommendations, IOH can significantly improve their customer service training programs, leading to higher service quality and customer satisfaction.