With over 400 million active credit card accounts on file, Apple had a prime opportunity to convert its customers using a sleek mobile payment system tied to the iPhone.

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Merchants that use Square Register are much more active than merchants who use the Square Card Reader: Register users are five times more active every week than those who use the Card Reader and they process about two times more revenue.

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In fact, most households have more than one credit card, and the average household has about four active cards, according to 2000 U.S. Census data.

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