Tips & Tricks for conditional iOS3, iOS3.2 and iOS4 code

A project or target that supports multiple versions of iOS

To make an application target that runs on multiple versions of iOS is relatively simple:

• Set the "Base SDK" in your projects settings to the newest version number of iOS whose features you may want.
• Set the "iPhone OS Deployment Target" to the oldest version number of iOS that you will support

However, getting the target settings correct is the easy part of the problem. The hard part is using new features on newer iOS versions without breaking the app on older versions.

Running in the 3.1.3 simulator

Detail at Original Source