San Francisco -- Despite a much publicized media leak of its next-generation iPhone, Apple CEO Steve Jobs still managed to rev up fans and developers Monday as he unveiled iPhone 4, a powerful successor in its smart-phone line. 'Stop me if you've already seen this,' Jobs quipped as he introduced the iPhone 4 to a packed audience at Apple's Worldwide Developers Conference in San Francisco. From his customary spot on stage, Jobs previewed the new, slimmer hardware, which comes equipped with a much improved screen, two cameras -- including one facing the user for video conferencing -- a faster processor, a gyroscope and a mobile version of Apple's video-editing program, iMovie. 'That is the iPhone 4,' Jobs said. 'We think it's the biggest leap we've taken since the original iPhone.' The phone, which will go on sale June 24 for $199 (16 gigabytes) and $299 (32 gigabytes), will also ship with the latest version of the iPhone operating system, now dubbed iOS 4. The new operating system includes multitasking, application folders, the iBooks e-reader app and a new mobile-advertising platform. IPhone 4 should provide a boost for Apple as it seeks to fend off rising competition from smart-phone competitors, most notably Google, whose Android operating system is powering a slew of iPhone rivals. There are three times as many iPhones in the market compared with Android devices, but recent quarterly Android sales are now similar to the iPhone. Many of the iPhone 4's larger hardware developments were predicted after gadget blog Gizmodo purchased a lost iPhone prototype in April for $5,000 and ran an exclusive story on the components of the new device. The story shed light on many of the new features, including the two cameras and a bigger battery, as well as the boxier look of the device. But Jobs summoned his ring-leading skills to highlight the specific advancements of the iPhone 4, saving until the end a new video-chat feature called FaceTime, which will enable users to easily conduct video calls at the push of a button. For now, the service will only work over Wi-Fi between iPhone 4 devices. 'I grew up dreaming of video calling and now it's real,' Jobs said. Jobs also spent a considerable amount of time showing off the iPhone 4's new display, which doubles the pixel density of the iPhone screen and eliminates the perception of pixels. At one point, however, Jobs ran into trouble during the demo when his device couldn't access Apple's private Wi-Fi network because of all the mobile Wi-Fi routers in use at the keynote. He actually paused and asked the bloggers in the audience to turn off their Wi-Fi to allow him to proceed with the demonstration. The new device will feature the same A4 processor powering the iPad as well as a new gyroscope that, when combined with the iPhone's accelerometer, allows the iPhone to work as a six-axis motion sensor. Developers believe the added sensor can bring about new applications in gaming. The iPhone 4's camera has been upgraded to 5 megapixels and includes digital zoom, an LED flash and advanced light-sensing technology that mimics the performance of dedicated cameras. The video camera can also shoot in 720p high-definition. Users will be able to stitch their pictures and videos into polished movies using a new $4.99 iMovie app. Much to the chagrin of some consumers, Jobs made no mention of a second iPhone running on Verizon Wireless, a popular rumor among Verizon users. The iPhone 4 will stay an exclusive of AT&T, which also replaced its unlimited smart-phone data plans Monday with cheaper but limited data tiers of $15 (200 megabytes) and $25 (2 gigabytes) a month. Avi Greengart, an analyst with Current Analysis, said the Gizmodo leak may have taken some of the surprise out of Jobs' keynote. But he said the details and execution in the iPhone 4 ensure the device is still the smart phone to beat. 'Just because a publication got some of the features doesn't mean it's not impressive,' said Greengart. 'I am very impressed. Apple was ahead to begin with and this just puts them further ahead.' Charles Golvin, an analyst with Forrester Research, said the new iPhone may sell more to existing iPhone users, rather than expand Apple's reach. But he said he was most impressed by the display and the FaceTime video technology, which Jobs said Apple was releasing as an open standard. 'If they can drive the adoption of video calling, we might finally see the realization of video telephony,' he said. For developers such as Ge Wang, founder of musical appmaker Smule, the inclusion of the gyroscope meant yet another tool for application programmers. 'This is definitely a step forward for Apple,' he said of the iPhone 4. 'It's not only the technology, but Apple's vision for the future. Clearly, Apple isn't standing still.' 