American Express announced today the availability of the American Express Pass for Passbook. Once you get it set up in the browser on your iPhone, the pass gives you your outstanding balance and last five charges.
With sensitive information like this now available on Passbook, it is important to check your settings for what is available without entering your passcode. To check, go to Settings > General > Passcode Lock. Once you enter your passcode, check the options under “Allow Access When Locked”. Personally, I have them all turned off.