There’s no debating that credit and debit cards are convenient, but typically the only places that you can use them are in businesses, or via the phone or internet. In 2009 the co-founder of Twitter, Jack Dorsey, set out to change that. He released a beta version of Square, a system that allowed mobile devices to receive card payments. A small card reader plugged into the device’s headphone port, and an app handled all the 1s and 0s. Two years later, Square is out of its debugging phase and available for general use.
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