foxfire235 has posted a video comparison of the displays on the Apple iPhone 4S, the HTC One X and the Nokia Lumia 900. A picture was taken with a high end Canon 5D Mark II DSLR and displayed using the three phones.
The Nokia Lumia 900 uses a ClearBlack AMOLED display. The HTC One X uses a Super IPS LCD2 display. The Apple iPhone 4S uses a IPS display.
The Lumia 900 and One X displays are clearly much better than the iPhone 4S display. In fairness though the iPhone 4S display use two year old technology, and it is fair to expect the next iPhone to have an improved display.