Nintendo Letter Box lets you create handwritten notes and then share those notes with other users on your friend list via the SpotPass™ and StreetPass™ features.
Nintendo might even send notes to you too! As your note collection grows and you spend Play Coins, you'll unlock new features and be able to personalize messages even further by changing stationery patterns, attaching photos and sound recordings, writing and drawing in 3D, and more. You'll even be able to surprise your friends with secret notes that they can only open on a certain date!
Passing handwritten notes to your friends is a breeze, regardless of whether they're sitting across the room...or across the world!