BII_Passbook_UsageBIIPassbook is Apple’s attempt at the virtual wallet.

Apple introduced Passbook alongside the iOS 6 operating system at its World Wide Developers Conference (WWDC) in 2012.

The iOS-only application is a platform for boarding passes, movie tickets, loyalty cards, and coupons. Whatever the format, it's considered a "Pass," in the world of Apple Passbook.

The Pass is typically but not always generated by another app — say Starbucks, or Delta Airlines. But the passes are organized within Passbook and accessed once the consumer needs to use them in the real world, via a scannable code.

Already, about 8% of all U.S. smartphone owners use Passbook, which means about 20% of iPhone owners use Passbook (since only two out of five U.S. smartphone owners use Apple handsets.)

Ever since its launch, speculation has gathered about Passbook's next step.

It's only one of several mobile wallet tools competing for consumer attention. Among its competitors are Google Wallet, Isis, PayPal Here, LevelUp, and others. And in one important way, it's the most limited of these services, because Passbook does not process payments itself.

So what's behind all the interest in Passbook?

There are over 500 million reasons: As of June, Apple had 575 million iTunes customer accounts, "most of them linked to credit cards," according to Apple CEO Tim Cook. In other words, it's estimated that Apple has more consumer credit cards on file than any other company in the world, thanks to the amazing reach of the iTunes store.

BII_Passbook_WalletPreferenceBII(Amazon is believed to have the second-most credit cards on file — we estimate around 160 million — but does not release that information. It has only reported in the past that 80 million consumers buy from its [...]