A report in May revealed that Apple was expected to launch an iPhone payments system with the iPhone 6 and iOS 8.

Subsequent reports echoed that same Information including naming Visa as a partner.  Re/code today reports that Apple has signed up a major American financial institution to work on its iPhone wallet program.
Apple has reached an agreement with American Express to work together on its new iPhone payments system, according to sources
familiar with the talks. American Express is one of several partners Apple will need to sign up before it can launch its new payments plan, which sources say it plans to announce at its September 9 product event.
Apple’s new payments system is expected to let iPhone 6 owners use their phone in place of a credit card or cash to pay for goods in brick-and-mortar stores. Customers will present their phones at the checkout counter of partnering retailers to transmit payment information to complete a purchase. It’s not clear which retailers have signed on to accept such payments.
Apple doesn’t have to re-invent the wheel here. Many U.S. stores now accept NFC-enabled Amex, Google Wallet/MasterCard Paypass, Visa Paywave and other electronic forms of payment besides the typical credit card swipe.

Source: 9to5Mac