It seems Apple’s Cards app and service for iOS is no longer available. The app allowed users to create custom made letterpress cards and have them mailed to the address of their choice.
As a replacement, Apple recommends creating letterpress cards on iPhoto for Mac.
Apple has confirmed that Cards has been discontinued as of yesterday, saying: “Cards ordered before 1 PM Pacific time on September 10, 2013, will be delivered, and push notifications will continue to work. You can view your previous purchases by tapping Saved Cards in the app.”