Operation of a satellite-based navigation-signal broadcast system receiver, such as a GPS receiver, on a wireless communications device is controlled by determining whether the device is stationary or in motion. Motion determination is accomplished by analyzing radiofrequency signal traces, e.g. GSM signal traces, received from one or more nearby base stations. A three-tiered analysis provides a progressively more accurate determination as to whether the device is moving or stationary while providing, in certain instances, a more rapid determination than prior-art techniques. When the device is determined to be stationary, the GPS receiver can be deactivated. When the device is determined to be moving, the receiver can be reactivated.