A portable communication device, such as a cellular telephone, communicates via a wireless communication link with a remote user interface device, such as a hands-free interface. The portable communication device and the remote user interface device each comprises a motion sensor, by which each device can determine motion of the device with respect to the earth. The devices may share, via the wireless communication link, motion messages. The wireless communication link may be terminated as a function of the motion of the devices. After the wireless communication link is terminated, the remote user interface device may automatically enter a low-power mode.