In case you missed it during all of your holiday revelries, Swapnote hit the e-Shop last week for free. It's sort of like Pictochat for the 3DS but it also supports 3D sketches, the ability to send to friends online and attach real images to your messages. It's pretty great.
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This Letter box \ Swapnote App is awesome ! Add me, 5284 1395 5564 and I'll send you a trippy 3D drawing :)