Since both apps are cross platform, this trick will work on Windows and Mac machines. All you need to do is open up iPhone Explorer or Phone Disk and navigate into the app's folder, located in
appname is the name of the app you want to change). Within that folder, find the png file that is the icon, named something like
[email protected]. Back that up and replace it with your own icon (you can usually find some good icons around sites like Iconspedia). Make sure the icon is in PNG format and is 114x114 pixels for iOS 4, 57x57 for iOS 3 and earlier. After rebooting your phone, you should see the old icon replaced with your new one.
Update: Originally, we said this method worked with previously mentioned Phone Disk. Due to the way iPhone Explorer organises the file system, the paths are actually different — we couldn't find the apps folders with Phone Disk, but if you download iPhone Explorer this trick should work as described. Sorry for the confusion.
Changing App Icons on the iPhone Without Jailbreaking [UNEASYsilence]