This application provides a communications system for improving a telephone call completion rate in an SA network and user equipment. According to solutions of this application, in a scenario in which calling UE resides in an LTE network or a 5G SA network and called UE resides in the 5G SA network, when the calling UE fails to call the called UE through an IMS domain, the calling and called ends cooperatively execute a call saving policy: The calling UE performs a call retry, for example, when a VoNR call or an EPS fallback call fails, falls back to LTE to initiate a VoLTE call retry, or initiates a CSFB call retry on LTE when the VoLTE call fails. The called UE falls back to the LTE network or a CS domain, and cooperates with the calling UE to complete the call. In this way, a probability that the UE successfully initiates a call can be improved, a call requirement of a user can be met, and call experience of the user can be ensured.