Sorry, I should have been more specific... Especially about the "why", because then it would be clear why a trackball for example wouldn't do.

One thumb use
A mobile device I want to operate with one thumb: holding it in one hand and using the thumb for everything. Now I don't want to give unnecessary details about the lengths of my body parts in this forum, but let me just say that I can comfortably move my thumb around an area of roughly 1.6"x1.6" (or 4x4cm). On a touchscreen device, this would mean a 2.2" screen that'll always be covered by my thumb.
(Go and watch people who use touchscreen phones, no matter which brand: They'll always hold it in one hand and tap on it with the other hand. That's a compromise I'll take for a portable device such as the tablet, but not for a phone that's supposed to be made for mobile use.)

Tactile feedback
I need to be able to operate the device without looking at it. It's a mobile device, so I do things with it while I walk, while I talk to somebody, etc.
With hardware buttons, I'm always certain what to do: One to the left, one down, press. Center, press. Quick look at the display, one up, press. You cannot do this with a touch screen.

Focus-driven UI
There's probably a better way to say this in English; what I want is that elements of the UI receive focus by clicking through them on a d-pad, the way in works on all cell phones I know, the way the "tab"-key works on a desktop GUI. This way, I needn't move a pointer across the display and hope I'll eventually hit the correct target (the way I do on a laptop with a trackball or a pad). Whatever can be activated/pressed will receive focus by pressing up/down/left/right on the d-pad. Only this way I'll be able to move through the whole GUI without looking at it, simply counting the number of clicks.

I'm fully aware that this will not cover all use cases a touchscreen (or even a trackball-driven pointer) would cover. You can't paint with a D-pad, can you? You cannot drag and drop with this method. (Well, you could, but a UI optimized for all this better not support drag and drop in the first place.) Still, it does what I need in a mobile phone so much better than a touch screen that I'm willing to accept these few drawback. (And I'm not an artist, anyway.)



I hope this explains better what I'd need, why I need it... And what would have to be changed in the UI to make using such a device a nice experience. (You wouldn't want to have dialogs, for example, with a lot of elements. That would make navigating through them with the d-pad annoying. It would be a lot like S60, in fact...)

I'm still not sure if it could be done technically. Could it work with the current GTK/Hildon framework with only minimal changes and a new HIG? Would be need to replace Hildon? Is it completly impossible with GTK? Is there something underneath the UI in Maemo that's so hardwired to the concept of a touchscreen device that it would take more than a change in the UI-parts to get this running? ...?