Installing previous iOS SDKs for XCode
Everybody wants to program with the latest and greatest iOS SDK don’t they?, or, perhaps you want to support the millions of people still using old iOS devices? Dust off that old iPhone 3G, and here is how to manually install a specific older version of an iOS SDK without re-installing XCode.
1. Download XCode and iOS SDK 4.2 from https://developer.apple.com/downloads/index.action
2. Mount the DMG by double clicking on it
3. Open a terminal window and navigate to /Volumes/XCode and iOS SDK/Packages/
4. Copy the *.pkg files to a folder on your desktop (cp *.pkg /users/you/Desktop/sdk)
5. Navigate to your new folder /users/you/Desktop/sdk
6. Unarchive the pkg file for the required iOS version, using xar -xf iPhoneOSxxx.pkg
7. Double click on the Payload file to unzip it.
8. Navigate to the iPhoneOS folder, and copy this to /Developer/Platforms/iPhoneOS.platform/Developer/SDKS/
9. Restart XCode
10. Select your new iOS version under Base SDK in project settings.