How to build an Xcode project with iPhone 3.1 or 3.0 SDK on an OS 3.0.1 device

To be able to build an iPhone app on a device with OS 3.0.1, you need to paste either of the following into Terminal:

• 3.1: ln -s /Developer/Platforms/iPhoneOS.platform/DeviceSupport/3.1\ \(7C116a\) /Developer/Platforms/iPhoneOS.platform/DeviceSupport/3.0.1\ \(7A400\)
• 3.0: ln -s /Developer/Platforms/iPhoneOS.platform/DeviceSupport/3.0 /Developer/Platforms/iPhoneOS.platform/DeviceSupport/3.0.1\ \(7A400\)

You might need to change the part of the paths highlighted in bold.

This should be all it takes to make your device show up in the Xcode organiser as being compatible with your SDK. You might need to restart Xcode for it to take effect.