While there may be some smart phone apps out there for the Nintendo 3DS AR Cards, you may not want to go that direction. Further, you may not have a smart phone with an available app. Because of that, I have taken each of the PDF versions of the AR Cards that Nintendo provides, and I turned them into JPG photos. Now, you can always take the cards with you. Place them in an iPhone photo album, move them to your digital camera, or even put them on a portable digital photo frame.
The images are all included in the .zip file below, and each are approximately 334×520 pixels.