A User Equipment (UE) including a wireless transceiver and a controller is provided. The wireless transceiver performs wireless transmission and reception to and from a first service network and a second service network. The controller receives a Radio Resource Control (RRC) message comprising a measurement configuration for SFN (System Frame Number) and Frame Timing Difference (SFTD) from the first service network via the wireless transceiver, performs first SFTD measurements between a Primary Cell (PCell) of the first service network and neighbor cells of the second service network via the wireless transceiver in response to the measurement configuration for SFTD indicating the neighbor cells, and sends a result of the first SFTD measurements to the first service network via the wireless transceiver.