Last year,

among small businesses, including food carts

Now,

reports, Portlanders use the device more per capita than any other city, including tech-savvy San Francisco, where the company is based.

The 1-inch-by-1-inch device, which converts an iPhone, iPad or Droid into a credit card reader with a three percent usage fee, is used by more than 30,000 Portlanders (compare with 25,000 in Seattle), according to spokeswoman Lindsay Wiese.

Since last year, the device has spread far beyond food carts. Brick-and-mortar businesses such as Salt & Straw ice cream, Coco Donuts and Clive Coffee all use Square in their stores.

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