An electrical circuit for bi-directional power control between two devices, including a mobile communication card, an electronic device that connects to the communication card, the electronic device being either (i) a host device that operates independently of the communication card and also interoperates with the communication card, or (ii) a jacket for the communication card, wherein the jacket is a passive device that does not operate independently of the communication card, and circuitry connecting the mobile communication card with the electronic device, including a device on/off button operative to power the electronic device on and off, and a switch, wherein the circuitry uses a single connection line connecting the communication card, the electronic device, the device on/off button, and the switch, to enable the electronic device to automatically power the communication card on and off using the switch, in response to the electronic device being respectively powered on and off.