A roller chain transmission comprises a sprocket having at least first teeth and second teeth having different tooth forms, the first teeth and second teeth being randomly arranged, and the number of the second teeth not exceeding four times of the number of the first teeth. A user equipment establishes a communication session that comprises a voice component in a packet data network. In one embodiment, the card includes a resiliently displaceable cover member that automatically moves in and out of the aperture for proper use in various data readers.