A mobile payment system authorizes payment by sending a Short Message Service (SMS) text message or secure hypertext transfer protocol (HTTPS) request to a customer's mobile phone or mobile device requiring customer to respond by SMS or HTTPS. A SMS payment software-plugin is installed on a Point-Of-Sale (POS) terminal. When a customer requests to pay by SMS, the plugin is activated and the customer's mobile phone number and zip code or POS PIN are entered on the POS terminal. The POS terminal sends a request to a SMS payment system, which sends the SMS text message to the customer's mobile device. When the customer replies to the SMS message with an approval code, the SMS payment system uses payment information for the customer to create a transaction request to a bank authorization network. When the SMS payment system receives authorization, it notifies the POS terminal to complete the purchase transaction.