There's even a smaller screen with the same resolution as N800 (4.13" screen) in Toshiba Protege G900 (just 3" screen). ( http://www.gsmarena.com/toshiba_g900-review-185p2.php ). I think there's effort to make Linux run on that nifty device too.

WiBrain has a 4.8" screen at 1024x600... unfortunately it has a clunky body which is not pocketable. It's a shame cause Ubuntu runs really smoothly on that machine.