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 utilizing a first RAT or a second service network utilizing a second RAT. The controller sends an indicator of a connection release request to the first service network via the wireless transceiver in response to terminating a first communication service with the first service network or in response to leaving the first service network for the second service network. Also, the controller releases a Radio Resource Control (RRC) connection with the first service network after sending the indicator of the connection release request.