Cellular phone subsidy lock

Abstract

A cellular phone subsidy lock which ensures that a cellular phone, sold to an end-user at a price subsidized by a cellular carrier, is activated only on the subsidizing carrier's network, and not on a competitor's network. A secure carrier code, specific to and known by the subsidizing carrier, is programed into the cellular phone by the phone manufacturer. The phone is programmed and shipped by the manufacturer in a locked condition, which prevents programming of the NAM (Number Assignment Module) of the cellular phone without first entering either a valid unlock code or a valid remove lock code. At the time of phone activation and programming of the NAM, the phone's ESN (Electronic Serial Number) is entered into the carrier computer system, which utilizes the ESN and carrier code to execute a subsidy lock algorithm which outputs an unlock code and a remove lock code. At the carrier's choice, either code is given to the end user to be entered into the phone. The phone then executes the same subsidy lock algorithm, using the carrier code programmed at the time of manufacture, and it's own ESN, to calculate the unlock code and the remove lock code. If the code entered by the user matches the unlock code, NAM programming is allowed to proceed only once, and if the entered number matches the remove lock code, the phone removes the subsidy lock completely.