BTW, they are using basically the same mechanism (credit card + online account + scanner + barcode on mobile phone screen) as I proposed back in April 2009... Thank you for appreciating and implementing this idea!
As a "side effect", this mechanism solves the credit card security problem because the customer's mobile phone and the merchant's point of sale are exchanging data using tokens rather than actual sensitive cardholder information which never touches the merchant's store systems or customer's mobile phone during transaction processing.