Here are quick startup steps for anyone interested in developing iPhone Apps.
1. First of all you need Mac machine either laptop or desktop. Apple SDK (called as XCode) only works on Mac machines.
2. Go to https://developer.apple.com/xcode/ and login with Apple Id (if you dont have one, sign up for free) and download XCode for free.
3. xcode is SDK for iOS apps development, it contains all necessary tools to develop, test and publish your application to live.
Note: you dont need to register with apple IOS app development program right away to start learning or developing applications.
4. Start enjoying development…. all you need xcode which comes with simulators to test the application in IPhone, IPad various versions.
5. Once you are ready to promote the applicaiton live (i.e in ITunes, ITunes App store is the place for IOS device apps), you need to have enrolled in IOS App development program. Now you can register/purchase the program (currently it costs 99$ per year)
Note: When i registered for the program in 2009 it took around two weeks to get approved as myself registered Independent developer. So better give some lead time for this registration process.
6. Once you upload the application you can check the status of application via ITunes connect (ITunes connect is the developer portal for managing application) – https://itunesconnect.apple.com
7. Apple might contact you with any questions before approval… if everything goes well, it can be live very soon.
For further reading refer iOS App Development Category posts.