I had a chance to review the passbook programming guide from Apple and I will mention the salient features of the protocol here. The APIs provide allow for registering a device to receive push notifications for a pass, getting serial numbers for passes associated with a device, getting the latest version of a pass, unregistering a device and for logging errors. These are used by Passbook to communicate with the web server of the company that generates the passes. The application that creates the passes may also be made available for download by the company