Possible Duplicate:
How to accommodate for the different screen resolution of iPhone 4?
What does the new resolution mean for existing applications?
Do the devtools make it easy to support new resolutions without changes, if so how? what happens to apps by those developers who dont do things properly to leverage this?
What are the rules for resolution compliance for app acceptance on the app store?
The new OS should (As Steve Jobs stated during the keynote) detect whether or not the app is built for the new res and scale accordingly. The new resolution is just double the old, so it should be a simple scale-up on the operating system's end.
All of the current UI elements will support the new resolution once iOS4 is released, so all a developer will have to do is update their custom images.
According to page 75 of the latest (2010-06-04) iPhone App Programming Guide.pdf:
On devices with high-resolution screens, the
imageNamed:,imageWithContentsOfFile:, andinitWithContentsOfFile:methods automatically looks for a version of the requested image with the @2x modifier in its name. It if finds one, it loads that image instead. If you do not provide a high-resolution version of a given image, the image object still loads a standard-resolution image (if one exists) and scales it during drawing.When it loads an image, a UIImage object automatically sets the size and scale properties to appropriate values based on the suffix of the image file. For standard resolution images, it sets the scale property to 1.0 and sets the size of the image to the image’s pixel dimensions. For images with the @2x suffix in the filename, it sets the scale property to 2.0 and halves the width and height values to compensate for the scale factor. These halved values correlate correctly to the point-based dimensions you need to use in the logical coordinate space to render the image.