I seriously gotta wonder how the iPhone of some random person (which has various third party apps on it, etc.) is going to meet the kind of security requirements the card issuer cares about: http://en.wikipedia.org/wiki/Payment_Card_Industry_Data_Secu...
This image on their home page gave me chills, though. http://a1.sqimg.com/static/6c1cc3c1ad109e13d0be182c75c470762...
But that's likely only because I'm a half-paranoid security geek.