Nintendo released a small update to their Swapnote application this morning which can be activated either from the eShop or the application directly. Swapnote will send you right to the eShop update page.
The software update now available for the message-sharing application will allow users to attach photos and audio recordings when replying to notes, take photos or record audio from within the application, use a different pen color on each page and undo their last pen strokes. The update will also offer faster load times.

Other advances in the application through the update are the ability to filter notes by users or favorites, choose whether to receive special notes on a category-by-category basis and delete multiple notes at once.

I personally have never used the Swapnote application but opted in to the note anyway. You never know, I may find a use for it one day.