When purchasing an item or service, a user enters a PIN enter their mobile communication device and send the PIN, e.g., via text message to a payment authority. The payment authority authenticates the user using at least the PIN and the mobile communication device identifier associated with the user's mobile communication device. If the user is authenticated, then the payment authority will send a transaction code back to the user, which will be displayed on the user's mobile communication device. The user can then provide the transaction code to the merchant. The merchant can enter the transaction code into the Merchant's point of sale system and complete the transaction.