IPhone 4 models. In fall 2010, pentalobe screws started to replace the Philips screws used in post-repair units in the US and in production units in Japan. The iPhone 4 shipped with iOS 4, which was the newest version of Apple's iOS mobile operating system at the time. iOS 4 introduced a multitasking system, allowing apps to remain "suspended" in memory, perform certain operations in the background, and allowing users to switch between apps using an on-screen menu. It also introduced FaceTime, which allows users to perform video calls between other iPhone, iPad, iPod Touch, and OS X users. The iPhone 4
IPhone be accessed by a hardware button below the screen on all models expect for the iPhone X where the user must swipe up. The original iPhone contained the following apps: Messages (SMS and MMS messaging), Calendar, Photos, Camera, YouTube, Stocks, Maps (Google Maps), Weather, Voice Memos, Notes, Clock, Calculator, Settings and iTunes (store). The App Store was introduced for the iPhone 3GS and iPhone 4. Compass, FaceTime and GameCenter were added in iOS 4 and 4.1 respectively. In iOS 5, Reminders and Newsstand were added, and the iPod application was split into separate Music and Videos applications. iOS 6 added