A mobile communications device with a wireless module and a controller module is provided. The wireless module performs wireless transceiving to and from a first cellular station of a first service network and a second cellular station of a second service network, wherein the first service network is a long term evolution (LTE) network and the second service network is a Universal Mobile Telecommunications System (UMTS) network. The controller module receives a measurement request message from the first cellular station via the wireless module, performs a measurement on the second cellular station in response to the measurement request message and reports the measurement result to the first service network via the wireless module, wherein the second cellular station is previously not requested or configured by the first service network to be measured.