It has been discovered that the digi-cards have been on sale through Nintendo of Japans online store recently and out of interest here's how much they cost:

The SD Digi-Cards, for the unaquainted, can be pluged into a PC which will allow the intriguing possibility for gamers to send game data to each other and even download events. Animal Crossing e+ will be the first game to exemplify their use in which they will allow data to be e-mailed between you and your friends and allow pictures to be taken with your PC.

There has been an official site launched for Animal Crossing e+ which will can be viewed here.

For more on the cards you can take a gander here too.