One of the major features in the iPhone 4 is the new camera, a 5-megapixel model that comes with a LED flash. This is a significant improvement over the 3-megapixel one from the iPhone 3GS and the 2-megapixel camera on the 3G and the 2G.
Still, while other rivals like the Samsung Pixon and the Nokia N8 offer 12-megapixel cameras, we found out that the one on the iPhone 4 was more than adequate and leapfrogs the current iPhones when it comes to quality.
Below is a comparison of the three cameras aiming at the same subject, the top of St Paul's cathedral in London, with an overcast sky. The 5-megapixel camera is way better than the two other models with the iPhone 3G fairing particularly badly.
Note that the images have not be retouched apart but only resized to fit the page. No flash was used and all the phones were on default settings. Thanks to Simon and Alex for lending me their phones.