Based on estimates charted for us by BI Intelligence, Apple is nearing a billion iTunes accounts on file, and that number is likely to surge immensely. Customers in China can now link their UnionPay payment cards to their Apple IDs: For context, UnionPay is the largest card network in the world with more cards in circulation than Visa and MasterCard combined. (Not on this list: Uber, which has north of 12 million payment cards on file.)