Image: iPhone 5 part with bigger display leaks online

UPDATED: It is speculative if the front panel picture below is the real deal, but we were tipped that LG actually has demonstrated a 4" IPS-LCD display with the mind-boggling 394ppi, so if the rumors about a 4-incher iPhone hold water, Apple probably has in mind precisely this UHD (for Ultra High Definition, we guess) display in mind for it. Thanks, Kevin!

A Chinese parts reseller has posted for the world to see what it claims to be the front panel of one of three alleged prototypes being tested of the next Apple iPhone.

The panel is said to have an opening for a 4" display, and we guess the other two models being tested are one with the standard 3.5-incher, and one for the cheaper iPhone we heard so much about already. The bezel also looks way thinner, especially on the sides, so the overall dimension might not change much.

Regardless if this thing is true or not, Dr. Soneira from DisplayMate, who is often cited regarding the qualities of mobile screens, states that in order to keep the same resolution of 640x960 pixels for a 4" display, the pixel density will have to go down. The 3.5" screen on the iPhone 4 has 326ppi, and the threshold for calling it a Retina Display is unofficially around the 300ppi mark.

If the next iPhone has a version with a 4" screen, and keeps the same 640x960 resolution, it will go down to about 285ppi, which is below the Retina Display specs. Not that it is dealbreaker, except for marketing purposes, considering the next best thing currently on the market is the 540x960 qHD res of the Motorola ATRIX 4G, which, however, is rumored to have the PenTile matrix arrangement that effectively lowers the official resolution, since it uses less subpixels per pixel to achieve it.

If Apple wants to keep the 300ppi + specs, it will have to grow the res to 1097 pixels, which will really mess up with what most apps for the iPhone 4 are targeting. Or, alternatively, it can be bumped on both sides to 768x1024 pixels (iPad's resolution), and achieve 320ppi. Is it possible and worth it doing that, as opposed to just not calling the alleged 4-incher Retina Display anymore? We'll leave that for Apple to decide.

LG has demonstrated an IPS-LCD last summer, of the 3.98" size, with 394ppi, and has named it UHD display, so if a 4" iPhone is to appear this summer, and the display can be mass produced on time, this one is most likely to appear in it. It would mean an impressive 1000+ pixel count both horizontally and vertically, so we can't wait for more leaks (or tips) to shed some light on that.