A communication apparatus including a radio frequency (RF) circuit coupled to a digital processing circuit and an interface circuit coupled to an authentication device. The RF circuit may be configured to operate on a radio frequency signal. A portion of the digital processing circuit may be disabled during an active mode of operation of the RF circuit. The interface circuit may be configured to buffer data communicated between the digital processing circuit and an authentication device during the active mode of operation of the RF circuit. In one embodiment, the interface circuit includes a memory and memory control logic to buffer data available for transmission to and/or received from the authentication device. In some embodiments, the digital processing circuit includes a processing unit configured to process authentication data received from the authentication device. In these and other embodiments, the authentication device may be a subscriber identity module (SIM).