It's otherwise doable (and actually was already done a couple of years ago), but since the N900 screen doesn't support multitouch it's only fully playable using the keyboard. (Most players will want to use both flippers at the same time.) This, in turn, pretty much means landscape only gameplay which will most likely put off some people. The PSP version did support portrait as well though but that was much more suitable for the PSP because of its button layout. On the PSPgo, which has a sliding screen like the N900, the controls were rather awkward in portrait. Because of these reasons it was not seen feasible to release an N900 version but to go for the N9 instead.