Simple way:
Apple SDK Download site, download it and reinstall.
http://developer.apple.com/iphone/index.action#downloads
Snow Leopard Downloads
* iPhone SDK 3.1.3 with Xcode 3.2.1
* iPhone SDK 3.1.3 with Xcode 3.2.1 Readme
Open your terminal. do it.
ln -s /Developer/Platforms/iPhoneOS.platform/DeviceSupport/3.1.2\ (7D11)/ /Developer/Platforms/iPhoneOS.platform/DeviceSupport/3.1.3
Refrence:
iPhone OS 3.0 SDK and iPhone OS 3.0.1 software release for
Mac OS X v10.5.7
To continue development with iPhone SDK 3.0 on your iPhone, iPhone 3G and
iPhone 3GS running iPhone OS 3.0.1 will need to perform the following:
1. Log into your Mac with an Admin account and launch the Terminal application
(/Applications/Utilities)
2. Copy and paste the following line into Terminal:
ln -s /Developer/Platforms/iPhoneOS.platform/DeviceSupport/3.0\ (7A341) /
Developer/Platforms/iPhoneOS.platform/DeviceSupport/3.0.1
Note: If you installed iPhone SDK 3.0 somewhere other than the default /Developer
location, replace the "/Developer" directory as appropriate.
© 2009 Apple Inc. All rights reserved. Xcode, Apple, the Apple logo, Mac, Mac OS, and Macintosh are
trademarks of Apple Inc., registered in the U.S. and other countries.
ln -s /Developer/Platforms/iPhoneOS.platform/DeviceSupport/3.0\(7A341) /Developer/Platforms/iPhoneOS.platform/DeviceSupport/3.0.1