We develop a vulnerability detection module to identify three important security vulnerabilities in the IMS system that supports 4G/5G multimedia services. We have validated them in 4 carriers from TaiwanU.S. using smartphones from 7 brands,shown that they can be exploited to launch a stealthy call DoS attack, a social engineering attack with ghost calls,a call ID spoofing attack. Moreover, attackers can detect attackable users using an AI technique with only the users＇ phone numbers. We finally propose solutionsdevelop an AI-based technique of call ID spoofing detection.