High resolution display is one of the important feature in iPhone 4.It’s resolution is double than that of the standard iPhone resolution.To implement this you don’t need to change any line of code in your project, the only thing you have to do to create two resolutions of resource images i.e the standard and high resolution and append @2x to the name of the high resolution image name and iOS 4 will automatically use the high resolution version if on an iPhone 4 and the low resolution version on the 3G .