A call control method, a communication system, and relevant devices are provided so that communications can be implemented under different network conditions based on the same number. The method includes: receiving a call request of a calling terminal, where the call request carries a called terminal number; querying a Home Location Register (HLR) of a called terminal according to the called terminal number; obtaining a Supplementary Service Code (SS_Code) from the HLR, where the SS_Code carries a Mobile Station International ISDN Number (MSISDN)-based IP Multimedia Subsystem (IMS) service identifier; and triggering an Application Server (AS) to implement an MSISDN-based IMS service according to the MSISDN-based IMS service identifier. A communication system and relevant devices are also provided.