An authentication method that can be used by a telematics-equipped vehicle to authenticate an SMS message and provide additional security features above and beyond those inherent to the SMS protocol. Generally speaking, a call center uses a mathematical function to derive a security code, and then sends an SMS message to a telematics-equipped vehicle that includes information related to the derived security code. The telematics-equipped vehicle can utilize the transmitted information to authenticate the sender of the SMS message and/or its contents. One group of suitable mathematical functions utilizes keyed-hash message authentication codes (HMACs).