Apple has added more vendors to its Passbook
digital certificate program, including the first credit-card reward redemption option. While American Express
lets users check their balance and transaction notifications, Discover has updated its iPhone app
to convert CashBack Bonus rewards into digital certificates that Passbook can store and redeem at various merchants. In addition, version 4.10 of the app now lets users make payments, send money using PayPal Messenger, search transactions and refer friends to Discover, which earns extra points.