Abstract: A transaction processing system uses a mobile phone to make payments at point of sale (POS), over the internet, and over the phone, and also to make money transfers. Transaction security is provided by using various combinations of authentication using the mobile phone. Account numbers linked to payment cards, and public/private keys that encrypt/decrypt customer data, dynamically change on mobile phone and a server, based on a specified number of transactions or time interval. No credit/debit account information is shown on mobile phones. GPS location and time stamps facilitate identification of unusual shopping patterns during internet and over-the-phone transactions. Customers can remotely delete data on mobile phone in case of loss. Three-level security used at POS combines industry-standard encryption; dynamically-changing account numbers and keys; and visual identification of customer, followed by software signature recognition.