The iPhone 4 is a smartphone that was designed and marketed by Apple Inc. Following a number of notable leaks, the iPhone 4 was first unveiled on June 7, 2010, at Apple's Worldwide Developers Conference in San Francisco, and was released on June 24, 2010, in the United States, United Kingdom, France, Germany and Japan. It is the 4th generation of iPhone, succeeding the 3GS and preceding the 4S. The iPhone 4 introduced a new hardware design to the iPhone family, which Apple's CEO Steve Jobs touted as the thinnest smartphone in the world at the time; it consisted of an uninsulated stainless steel frame which doubles as an antenna, with internal components situated between chemically strengthened aluminosilicate glass. The iPhone 4 also introduced Apple's new high-resolution "Retina Display"; while maintaining the same physical size and aspect ratio as its precursors, its liquid crystal display had a pixel density of 326 pixels per inch. The iPhone 4 also introduced Apple's A4 system-on-chip, along with iOS 4—which notably introduced multitasking functionality and Apple's new FaceTime video chat service. The iPhone 4 was also the first iPhone to include a front-facing camera, and the first to be released in a version for CDMA networks, ending AT&T's period as the exclusive carrier of iPhone products in the United States. It was succeeded as Apple's flagship smartphone in 2011 by the iPhone 4S. However, iPhone 4 continued to be produced until 2013. The iPhone 4 received generally positive reception, with critics praising its revamped design and more powerful hardware in comparison to previous models. While it was a market success, with over 600,000 pre-orders within 24 hours, the release of the iPhone 4 was plagued by highly publicized reports that abnormalities in its new antenna design caused the device to lose its cellular signal if held in a certain way. Most human contact with the phone's outer edge would cause a significant decrease in signal strength. The iPhone 4 spent the longest time as Apple's flagship iPhone model at fifteen months, and had the longest lifespan of any iPhone ever produced, spanning close to four years and available in some developing countries until early 2014.