A method and apparatus for processing an IMS terminal's call request for real-time service and non-real-time service received over an IMS domain in a CSI terminal. When deciding to use a CS call for real-time service and an IMS session for non-real-time service, the CSI terminal sends an IMS session response for the non-real-time service. In the mean time, the CSI terminal generates a CS call request for the real-time service and sends the CS call request to an AS in an IMS domain. The AS sends the CS call request in association with the IMS session response to the IMS terminal, thereby completing a call setup. For the association, the AS sends its MSISDN to the CSI terminal and identifies from the MSISDN included in the CS call request and the IMS session response that the two messages are related to the IMS terminal's call request.