What are the specifications for the icons required by Apple for a custom iPhone application published?
57x57, PNG, No Transparency, No Layers, 72 PPI
512x512, TIFF or JPEG, No Transparency, No Layers, 72 PPI
Note: iPhone OS applies rounded corners, optionally shine, and other effects
Also have a large version of your logo with the name of the application in case Apple contacts you needing a version for marketing purposes.
From here:
To ensure that your icon can take advantage of these visual enhancements, provide an image in PNG format that:
Name your icon file Icon.png and place it at the top level of your application bundle.
The app store is looking for a 512x512 icon as well (not sure the PPI). Best bet is just to design it as vector then you can easily resize and export it as whatever.
The icon should be a 57x57 pixel PNG. The PNGs generated by Apple have a PPI of 72.01 so I guess something in that range will work fine. Don't have a very high PPI else images are not rendered properly.
If you want to use a custom icon and not let the iPhone to apply the gloss to your icon, add a key to info.plist called UIPrerenderedIcon (is a boolean value) and make it checked.
When submitting the app to the app store, you will need a 512x512 pixel version of your app's icon (this one in jpeg or tiff format) and at least one screenshot of your app. You can have additional 4 screenshots of the app.
57x57 pixels png... you can choose via code to apply or not the gloss effect. Google helps > http://www.iphoneiconsize.com :)