A method includes receiving, by a mobility management network element in a first network, first information from an access network device in the first network, where the first information indicates a handover of a terminal device from the first network to a second network, and sending, by the mobility management network element in the first network, second information to a mobility management network element in a third network based on the first information, where the second information instructs the mobility management network element in the third network to send a handover request to a mobile switching network element in the second network, and the handover request requests to hand over a voice service of the terminal device to the second network.