Open Toolchain  is for the development of 1.x native application for iPhone, It can be used in Mac OS X (Intel/PPC) 10.4/10.5, Linux, Cygwin or MinGW. This SDK uses gcc cross compiler for the development.
Build from sources method:
- http://code.google.com/p/iphone-dev/wiki/Building for Mac OSX 10.4 (PPC/Intel) / Ubuntu / Fedora / Gentoo / Debian / CentOS / XP Cygwin / XP MinGW
- http://wikee.iphwn.org/howto:toolchain_on_leopard for Mac OSX 10.5 Leopard
There are also Pre-build Binary for different Operating System (OS) and CPU
- WinChain (Only for Windows XP) WinChain Download from this ftp site
- Binary ToolChain Installer (Only for Mac OS X 10.4 Tiger and Intel CPU) Download from here
- iPhone Toolchain VMWare Debian Linux Image [use for VMWare Player / VMWare Workstation (win) / VMWare Fusion (Mac)] VMWare Debian Linux Image Download from this ftp site
There were some changes in 1.1.2/3 API, toolchain header files should also be updated
iPhone SDK is the offical development tools from Apple Inc for iPhone Developer to develop firmware 2.0 Native Application. It is only available for Mac OS X 10.5.2 and Intel CPU (see ppc hack here).
The latest iPhone SDK beta 8 can be downloaded from Apple iPhone Developer Website,
Previous version of iPhone SDK can be downloaded from this ftp site. After installation of the iPhone SDK, all the sample codes of that version of SDK can be obtained from harddisk. They are in
There are numerous limitations  for iPhone SDK in development of official iPhone software, Therefore iPhone Dev Team provides a how-to use iPhone SDK with Open Toolchain API
It is now also possible to build firmware 2.0 app without using the official sdk and Mac OS. Read this article - Upgrading the iPhone Toolchain
Apple Inc has also provided iPhone Web Application documentation, but it is less attractive than Native Application.
To build iPhone Native Application for 2.0, you can
- Join the Apple iPhone Developer $99 program and follows the offical SDK API
- Install the Open toolchain headers and the Xcode Template as per instructions here