According to one embodiment, a data storage apparatus includes a write command module, a read command module, and a controller. In one embodiment, a cellular device produces a communication session key and utilizes an index and corresponding timing intervals previously provided by the network to the cellular device. The bias circuit generates a third current by adding the first current to the second current, and outputs the bias current that is the third current or a fourth current depending on the third current. A switch receives a call request from a calling user and on determining that a communication session cannot be established between the calling user and the called user, the switch terminates the link to the calling user and sends the call attempt notification to the called user.