It has been possible for quite a while to draw on the screens of an assortment of touch-screen phones and PDAs.
Drawing and painting directly on a screen, however small, is of course much easier than doodling on a graphics tablets set at the side of a desktop, let alone with a mouse. All the same, at the start, even the crudest sketching was barely possible. I did manage a little owl with the joystick on a Sony Ericsson T610 I once had.

It was easier to draw on my Palm Treo phone, though the coarse resolution of the Treo 600 screen still made drawings look jagged and blocky. I gather the Treo 650 and 700p had higher resolution, but still created only tiny pictures. For Palms you could get any number of add-on art editors, of which the best was Teal Paint.
Pocket PCs offered a more versatile range of add-on art software. Pocket Artist and the older Idruna Photogenics at one time seemed almost mini-Photoshops in themselves!

I called this picture GoldenEggs. I added the frame in Photoshop and sent it as a Christmas card. It was a scribble with various effects in Idruna Photogenics on my Pocket PC.
When you drew in Pocket PC Notes, which came with the machine, you were doing vector drawing, which allowed for handwriting recognition as well as artistic creations. It was fun to try the face game to get the hang of this different kind of drawing.
MAKING FACES ON A POCKET PC

Now (I'm revising this page in 2010) I do a good deal of painting on my iPhone. I found it hard at first to paint with my finger rather than with a stylus, but soon got used to it. I bought a Pogo stylus but rarely use it now.
Drawing on phone or PDA