This mock-up was drawn for i48 the HP48GX emulator from Automagic-Software:
http://www.automagic-software.com/products/i48/

It's based on the long defunct Power48 on the Palm TX.

The main targets were:
- sharpness of both the screen and the keyboard.
- center keyboard for users of iPhone/iPod cases.

Possible enhancements:
- larger keyboard to use the real estate.