https://purengom.com/2010/06/22/iphone%ec%9d%98-%ec%9a%b4%ec%98%81%ec%b2%b4%ec%a0%9c-%ec%83%88%eb%a1%ad%ea%b2%8c-%eb%b3%80%ec%8b%a0-ios-4-%ea%b3%b5%ea%b0%9c/
iPhone의 운영체제 새롭게 변신! - iOS 4 공개