Apple has posted a new version of the iPhone Software Development Kit, in light of the iPhone OS 2.2 release last week. Developers are encouraged to download the new version of the SDK, as it is optimized for work on devices with firmware 2.2 installed.

Listed as build 9M2621, the updated SDK is almost 1.6GB big – considerably larger than previous releases. The new version of the development kit requires Mac OS X 10.5.5, the latest version of Leopard available. Needless to say, the SDK also runs solely on Intel machines.

By using the iPhone Software Development Kit, developers can produce iPhone and iPod touch-compatible applications, which they can submit to Apple for approval, on the iTunes App Store. However, some of the rules surrounding iPhone development posed obstacles to some developers. Therefore, on October 1st, Apple decided to remove the non-disclosure agreement (NDA) for released iPhone software. The updated iPhone SDK agreement is now posted on the iPhone Dev Center, providing developers with a new start, so to speak.

Developers can choose to download the SDK (as long as they have an iPhone Developer account – free), and develop apps on their own. Those with bigger plans in mind can enroll in Apple's iPhone Developer Program ($100 a year), which provides a complete and integrated process for developing, debugging, and distributing free, commercial, or in-house applications for iPhone and iPod touch. Complete with development resources, real-world testing on iPhone, and distribution on the App Store, the iPhone Dev Program makes the fastest way to get an idea onto handsets worldwide.

The iPhone SDK also includes the cool iPhone Simulator, a virtual environment that simulates the iPhone perfectly. This allows developers to test their apps in real time, as they develop them – write one more line of code, then drag the app over the iPhone sim to see how it works. So that's the iPhone SDK for you, and below you have the new version available for free download.

Download iPhone SDK (Free)