如果你瞄準的是iOS 3,那麼你最終將不會使用大多數iOS 4的功能。
這是蘋果的聲明。
瞄準最新的iOS版本。
Targeting the latest release allows you to take advantage of all the features
available in the latest version of iOS. However, this approach may offer a smaller
set of users capable of installing your application on their devices because your
application cannot run on iOS releases that are earlier than the target release.`
目標更早的IOS版本。
Targeting an earlier release lets you publish your application to a larger set of
users (because your application runs on the target OS release and later releases),
but may limit the iOS features your application can use.`
但我建議你瞄準了iOS 4的人現在瞄準的iOS 5,而在另一個8個月,我相信蘋果將發佈iOS 6中(他們是非常快與他們的更新),而且我個人認爲,針對iOS 3的長期運營並不會帶來很好的結果。
閱讀此[回覆](http://stackoverflow.com/questions/3027120/how-to-make-iphone-app-compatible-with-multiple-sdk-firmware-versions/3027213#3027213)關於兼容性多個iOS版本 – progrmr