Abstract: A method is disclosed for operating a mobile station (10) that includes the steps of (a) storing in the mobile station a SPC derived at least in part from a multi-bit secret pattern that is stored in the mobile station for use in a mobile station authentication process; (b) entering a SPC into the mobile station; (c) comparing in the mobile station the entered SPC to the stored SPC; and (d) only if the entered SPC and the stored SPC are found to be equal, enabling a desired function to be performed. The multi-bit secret pattern is preferably an A-key, and the SPC is preferably a checksum derived from an algorithmic combination of the A-key and an electronic serial number of the mobile station. The SPC may also be derived from at least one further mobile station parameter, such as the mobile station identification number (MIN) or the international mobile station identity (IMSI).