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 to the iPod Touch as "training wheels for the iPhone". All iPods lack Touch ID, 3D Touch, NFC, GPS, an earpiece speaker and a noise-cancelling microphone. Depending on the generation, the iPod Touch may have a smaller or inferior display and camera(s). Newer models (5th and 6th generation) lack the ambient light sensor that makes automatic brightness available. Older models lack a built in speaker, a microphone, a camera, and a flash. No iPod Touch has a modem through which it can place phone calls or send SMS and MMS. However, 5th and 6th generation models can either piggy-back on