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 instruction leaflet, but as with many newer iPod models the battery in the first generation iPhone has been soldered in. Therefore, a soldering iron is required to install the new battery. The iPhone 3G uses a different battery fitted with a connector that is easier to replace. The iPhone X features a different battery, with two battery cells, and the adhesive pull tabs are adhered to the sides instead of folded over the top, therefore making repairs a little more difficult than before. A patent filed by the corporation, published in late July 2013, revealed the development of a new