Details of the next 3DS system update were announced today which is scheduled for release in December and is based on feedback from Nintendo fans and gamers, starting with a unified Network ID.
The Nintendo Network ID is something used only on the Wii U at the moment, but it means you have separate accounts for the eShop on 3DS and Wii U. The update will allow users to register the 3DS to their Nintendo Network ID, so you have one ID for both systems and one balance to buy games with.
If you don’t already have a Nintendo Network ID, you will need to create one, so that you can download content from the eShop. If you already have a NNID on a Wii U, make sure you register the same ID on the 3DS to combine the balances.
The ID is something needed for future services which includes Miiverse. Yes, Miiverse is coming to the 3DS which is available with the update. Your NNID is tied to your Mii which represents you in the Miiverse community.
More 3DS games will have communities on Miiverse in the future, meaning you can share images and information to other gamers.
All the information you need about Nintendo Network ID and Miiverse on the 3DS can be found on the Nintendo website.