deficiencies, the ROKR E1's firmware limited storage to only 100 iTunes songs to avoid competing with Apple's iPod nano. Cingular gave Apple the liberty to develop the iPhone's hardware and software in-house, a rare practice at the time, and paid Apple a fraction of its monthly service revenue (until the iPhone 3G), in exchange for four years of exclusive U.S. sales, until 2011. Jobs unveiled the first-generation iPhone to the public on January 9, 2007, at the Macworld 2007 convention at the Moscone Center in San Francisco. The iPhone incorporated a 3.5-inch multi-touch display with few hardware buttons, and ran the iPhone OS operating system with a touch-friendly interface, then marketed as a version of Mac OS X. It launched on June 29, 2007, at a starting price of US$499 in the United States, and required a two-year contract with AT&T. On July 11, 2008, at Apple's Worldwide Developers Conference (WWDC) 2008, Apple announced the iPhone 3G, and expanded its launch-day availability to twenty-two countries, and it was eventually released in 70 countries and territories. The iPhone 3G introduced faster 3G connectivity, and a lower starting price of US$199 (with a two-year AT&T contract). Its successor, the iPhone 3GS, was announced on June 8, 2009, at WWDC 2009, and introduced video recording functionality. The iPhone 4 was announced on June 7, 2010, at WWDC 2010, and introduced a redesigned body incorporating a stainless steel frame and a rear glass panel. At release, the iPhone 4 was marketed as the "world's thinnest smartphone"; it uses the Apple A4 processor, being the first iPhone to use an Apple custom-designed chip. It introduced the Retina display, having four-times the display resolution of preceding iPhones, and was the highest-resolution smartphone screen at release; a front-facing camera was also introduced, enabling video calling functionality via FaceTime. Users of the iPhone 4 reported dropped/disconnected telephone calls when holding their phones in a certain way, and this issue was nicknamed "antennagate". In January 2011, as Apple's exclusivity agreement with AT&T was expiring, Verizon announced that they would be carrying the iPhone 4, with a model compatible with Verizon's CDMA network releasing on February 10. The iPhone 4S was announced on October 4, 2011, and introduced the Siri virtual assistant, a dual-core A5 processor, and an 8 megapixel camera with 1080p video recording functionality. The iPhone 5 was announced on September 12, 2012, and introduced a larger 4-inch