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
IPod Touch date has been introduced with the same release number of iOS as the contemporary iPhone model. Successive updates to iOS since the initial release in 2007 have released additional features. iPhone OS 2.0, released on July 11, 2008, introduced the App Store, which allowed third-party applications for the first time. iPhone OS 3.0, released on June 17, 2009, added features such as cut, copy, and paste, data tethering and push notification support. iOS 4.0, released on June 21, 2010, introduced iBooks, FaceTime, and multitasking. It dropped support for the first generation iPod Touch. In June 2011, iOS 5, the fifth