LG has been the supplier of past iPhone displays, and is reported to keep that coveted position. The trouble is that the rumors don't fit with Apple's current "retina display". It is rumored that the iPhone 5 display will be 4" and have the same resolution as current iPhones at 640x960, but this would mean the screen would have 288 pixels per inch (PPI). The idea of a "retina display" is that the screen has a higher PPI than the human eye can discern, and the number for that given by Steve Jobs (which is under debate) is around 300 PPI. So, putting the same resolution in a larger display would remove the self-applied "retina display" name.
It seems unlikely that the iPhone 5 would keep the same resolution if it makes the screen bigger, because that would cause it to lose "retina" status, and there is almost no way Apple would give up that marketing chip.
source: Korean Times