@Fatalist - I have not tested Nintendo DS..
I am sure that any kind of paint app can be good to try and experiment with

and my personal opinion about what is the best way to learn "draw" is a simple tools like pencil and paper. I still carry traditional sketchbooks with me besides Nokia N900. I still have a lot to learn it is never-ending process and it should be fun process

daily.. done in Nokia N900 with MyPaint and edited in Nokia Lumia 635.