Apple has posted the preliminary version of the iPhone OS 4 Software Development Kit, also known as the iPhone SDK 4 beta, to its Developer Web Site. The SDK download is 2.9GB in size, with separate iPhone OS 4.0 operating system betas at roughly 300MB-400MB a piece. Apple’s OS betas are for 2008 and 2009 iPhone and iPod touch models only. They notably exclude the iPad, which is explicitly disclaimed as not compatible with “iPhone OS 4.0”, and 2007 iPhone and iPod touch models, which are not and apparently will not be supported by iPhone OS 4.
Apple posts iPhone SDK 4 betas for iPhone, iPod touch, not iPad

Jeremy Horwitz
Jeremy Horwitz was the Editor-in-Chief at iLounge. He has written over 5,000 articles and reviews for the website and is one of the most respected members of the Apple media. Horwitz has been following Apple since the release of the original iPod in 2001. He was one of the first reviewers to receive a pre-release unit of the device, and his review helped put iLounge on the map as a go-to source for Apple news.