I used a number of phones before and I do prefer "fold" formfactor to any other one. My idea is about this formfactor and completely new combination of two different touchscreens. Exactly I don't know any one such a phone yet.
Telephone must have 2 internal screens: precission resistive 480x800 screen on top fold half, and capacitive 240x320 multitouch screen on bottom fold half. Bottom screen must be used to control device by fingers, select objects, type words and numbers and so on. Images of controls can be different and can be changed dynamically. Top half fold screen used to show photos, videos, games, maps and so on... With good quality! That creates a compromise between different techniques: capacitive screen for fingers and resisitive screen for stylus. Fold formfactor allows use both techniques in one device. And in this formfactor device can be not so large when closed. Just imagine: 2 screens of about 4" in size - in a device with size 100x65 mm! And just imagine it's usability! You can draw on top screen, but select drawing tools from icons on bottom. Or you can watch photo with good quality on top screen and select from gallery on bottom... There are lots of possible improvments in this formfactor. I'd like have similar device RIGHT NOW!
External screen must exist too. I used Lenovo ET560 for years before. It was able answer the call using closed device, with just one button. I think this can be implemented in new device too.
And with Linux Maemo of course! Not like a "telephone" but like a "full functional pocket computer".