The free download is available online through the company's Apple Developer Connection Web site. The second beta of the SDK includes an interface builder, the Xcode integrated development environment, the iPhone simulator, frameworks and samples, compilers, and the Shark analysis tool.
Developers who want to test their code directly on the iPhone and distribute their applications through Apple's App Store have to apply for membership in the iPhone Developer Program.
Apple released the first test version of the SDK on March 6. Since then, developers have logged a number of complaints, starting with Apple's requirement that all distribution of applications to iPhone users go through the company's App Store.
More recently, developers learned that they won't be able to create music players for the iPhone. The SDK apparently doesn't permit access to iTunes, the iTunes library, or any facets of the iPhone's music player. As a result, music services such as Amazon.com and eMusic, won't be able to write their own download services for the iPhone.
Some developers, however, have been trying to make an end-run around Apple. Hackers calling themselves the iPhone Dev Team reported a couple of week ago that they found a way to run applications on the upcoming firmware of the iPhone and iPod Touch without a development certificate from Apple.
The company plans to upgrade the devices' firmware in June. The new software will have the hooks necessary to run applications built with the SDK.