If you are unsure of what passbook is it is an all-in-one application that allows you to keep all your giftcards and other money paying tenders all in one place.
The only problem I was having is that I would personally recommend having a jailbroken iPhone on iOS 5.1.1. Due to the current state of jailbreak being tethered I am not interested in having my computer drag along with me if i want to get my phone to boot back up.
If you have been reading recent apple news you would be know that ryan petrich has released the IOS 6 Maps.app port on Cydia.. So im sure everything can be worked on.
Anyways I am just asking for a passbook port and I am sure it can be achieved.
If no one decides to take on the project I will in November with my new MAC.
Stay Tuned!