This will be very neat. There have been some very cool paint apps for mobile devices such as the Iphone. I personally like Autodesk's SketchBook pro. Upload one of you favorite mobile drawings that you have created. It will be a little show and tell.
This city sketch I created on my Ipod Touch using SketchBook Pro. The hardest part was creating the perspectives, such as making the windows. One nice part of the sketch is the lights, as I was able to create a glow. I think I will go back and improve some areas such as try to make the city lights line up, which is really hard.