Apple has released iOS SDK and iOS 4.1 beta for its developers. They’re available from the iPhone Dev Center. Apps built with iOS SDK 4.1 beta should only be tested on devices running iOS 4.1.

Apple says to make sure to read the Xcode 3.2.4 Readme  ( and the iOS SDK 4.1 beta Release Notes  ( before installing and downloading these new releases. iOS is the operating system formerly known as the iPhone OS.