A mobile communication device supporting wireless communications using a first subscriber identity and a second subscriber identity is provided. The mobile communication device includes a Radio Frequency (RF) device and a controller. The controller is coupled to the RF device such that the controller performs the following actions: performing a first measurement on a cell via the RF device by using the first subscriber identity to obtain a first measurement result; determining whether the first measurement result is valid; and based on a result of the determining, performing a second measurement on the cell via the RF device by using the second subscriber identity to obtain a second measurement result.