What are the specifications for the icons required by Apple for a custom iPhone application published?
57×57, PNG, No Transparency, No Layers, 72 PPI
512×512, 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.