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 to its customers on its website, acknowledging the effect that old batteries have on the iPhone's performance. The company offered $29 battery replacements as a solution. The first-generation iPhone and iPhone 3G have a fixed-focus 2.0-megapixel camera on the back for digital photos. It has no optical zoom, flash or autofocus, and does not natively support video recording. Video recording is possible on the first-generation iPhone and iPhone 3G via a third-party app available on the App Store or through jailbreaking. iPhone OS 2.0 introduced geotagging for photos. The iPhone 3GS has a 3.2-megapixel camera with autofocus, auto white balance,