Apple has patented a new display technology that apparently will permit at least part of the iPhone's display to be on at all times with little cost to battery power. The new display system, which is apparently being readied for future versions of the iPhone, will use a secondary lighting system located underneath the primary lighting system which will allow pixel icons or cut-out icons to be lit at all times. The secondary lighting system will be low-power so that there will be very little battery draw down. This will enable at least part of the display to be on at all times, even when the main display is off.
But, frankly, all of this is guesswork based on Apple's patent application for the technology. Patent applications are full of technical and legal jargon, so it's really anyone's guess as to how the specifics will pan out in reality. But it does appear that something's up with making the display useful even when everything else is "off". Any other guesses?