In March of 2008, Apple released an SDK, or Software Development Kit, that allows independent software developers to design applications for the iPhone, write the programs and test the software to see if they will work properly on the iPhone.
IPhone owners can find all kinds of applications at the Apple App store. If you’re a developer, you can post your application for free or for a fee, depending on what you’ve put into it and what you want to get out of it.
It costs $99 to download the Standard SDK and $299 for the Enterprise version, or you can ask a company like Webdatamation to create an iPhone app for you.
SDK provides an environment for development tools that is similar to other Apple environments. Developers will find the source editor and graphical debugger look familiar and are intuitive to use.