Popular 3DS app Nintendo Letter Box (aka Swapnote) could have been the light of day on DSi, a new Iwata Asks reveals.

Members of the development team reveal the game was originally in the works as DSiWare and had entered the debug phase at the tail-end of 2009, but several limitations imposed by the console's firmware held it back, as director Daiji Imai from Nintendo's Network Business Department explains:

Even then, it was shaping up quite nicely. But it had a few weaknesses. For example, the Nintendo DSi system itself didn't have the Friend List 7, so we put that function into the software. But you could only register 18 friends. Another big weakness was that you had to manually access the server all the time to check whether you have received a diary from others or not. It was unavoidable that sometimes you would think, "Did it come in? Argh! It didn't!"

Programmer Satoshi Takenouchi also revealed that originally the application had more colours and levels of 3D, but these were removed to streamline the software:

We tried various kinds of 3D representation and multiple color pens. If you do that, though, the controls get complicated and it turns into software only for those with artistic skills. So I carefully selected what functions to include and placed emphasis on something that anyone could write easily, send right away, and use comfortably. As a result, I feel like it turned out to be something that many people can use.

Nintendo president Satoru Iwata is a big fan too:

You can exchange Play Coins for stationery. I've never felt so strongly before that I don't have enough Play Coins!

Not such a fan of walking, though.

[source iwataasks.nintendo.com]