As was reported before, Samsung has unveiled a 4.99" Full HD AMOLED panel (440PPI). This panel will go into production in Q1 2013, and will probably be used in their upcoming Galaxy S4 flagship phone:
Samsung managed to achieve such a high pixel density using a modified FMM technology. According to Anandtech, Samsung also adopted a new material that makes these AMOLEDs 25% more efficient. This means that Samsung finally adopted UDC's green PHOLED materials in the new panels.
It's still not clear what kind of pixel scheme is being used here - Pentile or RGB (or maybe modified-RGB as used in the Note II). The S3 has 306 ppi (4.8" 1280x720, PenTile) and the Note II has only 267 ppi, 5.5" 1280x720 - but without PenTile.
Actually Samsung uses three different schemes. Pentile, RGB Stripe and modified-RGB used in the Note II. If you look at the photo here, you'll see that the Note II display's blue pixels are twice as large as the red and green one. This is no regular side-by-side RGB as used in the Super AMOLED Plus displays for example (and in LCDs, too)
They called this arrangement "S-Stripe." So, if S-Stripe can achieve ~270 ppi, then the somehow "Pentilized" S-Stripe could possibly go beyond 400 ppi.
There is no "modified-RGB"... either it's Pentile or RGB, all of the rest is marketing. It seems to me that they are talking about Pentile this time too... Makes me wish they stayed with RGB, like S2... Pentile matrix makes white look blue... it is not what OLED was invented for. It is not good, they should lower resolution but make it RGB, even this would be good at this point.