Satoru Iwata acknowledges the popularity of the 3DS messaging app...

It may not be the quick-and-dirty instant messaging service that some people wanted it to be, but we'd like to think that Letter Box has earned itself the status of being a worthy addition to any 3DS owner's army of apps.

According to Nintendo president Satoru Iwata, Letter Box - known as Swapnote in North America - has become a hit worldwide, especially among women. He hinted that future updates would further incentivize people to make use of the free software.

"More than 10 million handwritten notes have been exchanged in the four weeks after the launch of the SwapNote service. And, I believe that the number of handwritten notes to be exchanged will increase at an accelerated pace if we can have users continue to enjoy the software for a long time. In fact, we have some plans to encourage more people to use it, and you will find out what I am talking about when we reveal such plans in the future."

Letter Box can be downloaded for free on the eShop. With it, 3DS owners can send friends 3D doodles, messages, sound recordings and 3D photos to each other via SpotPass.