Planet Computers Astro Slide 5G Transformer

I like the idea of this phone (and the Fxtec Pro1 needs some competition before all of their pre-orderers die of old age), especially the clever way they keep the screen visible either in open or closed slider modes.

Part of the thing I don't get though is why these companies don't do a 'plain' slider, like that on the Photon Q or Droid series of devices? Patent encumbrances, too boring for marketing?