With anticipation at a fever pitch, Apple CEO Steve Jobs unveiled the iPhone 3G to an appreciative audience during the opening keynote speech at the company's Worldwide Developers Conference on Monday.

The new iPhone, sporting a thinner and sleeker look, will support faster 3G (third-generation) broadband wireless networks and come with built-in GPS (Global Positioning System) capabilities, Jobs said. Support for 3G networks will enable the new iPhone to download data up to 2.8 times faster than the earlier model, Jobs said. Built-in GPS will make it easier for users to navigate roads.

The iPhone 3G will come with a 3.5-inch screen and have better battery life, with talk time of five hours, stand-by time of 300 hours, six hours of high-speed browsing time, 20 hours of audio and seven hours of video, Jobs said. Some who had previously bought iPhones complained about its battery life and that was a problem that Apple needed to solve with the new iPhone, Jobs said.

While Jobs said the phone is "even thinner at the edges," it is just a hair thicker than its predecessor. The 3G iPhone is 0.48 inch, or 12.3 mm, thick, while the previous version is 0.46 inch, or 11.6 mm, deep.

Quicker data downloads and lower prices are key to greater adoption of iPhones worldwide, Jobs said. Apple has cut the price by half to make the new iPhone more affordable for users, so that the 8GB model will sell for $199 (£101) and the 16GB model for $299. The company found that 56 percent of people surveyed wouldn't buy the earlier iPhone because they found it expensive.

The phone will ship on 11 July in North America and will eventually be rolled out in 70 countries, including India, China, Singapore and Australia, Jobs said.

The release ends months of speculation surrounding the iPhone 3G's release date and features. Apple earlier acknowledged that stocks of the original iPhone were low in the US and Europe, fueling speculation that Apple was winding down supplies to ready the market for iPhone 3G.

In the US, AT&T is ready for the new iPhone, announcing last week that it had upgraded its 3G wireless network with improved downlink speeds of up to 1.7Mbit/s, a 20 percent increase over previous speeds. The broadband network is available in many US metropolitan areas and the carrier intends to expand it. The network uses HSDPA (High Speed Downlink Packet Access) technology.

Jobs also said Apple will preview the new version of Mac OS X, codenamed "Snow Leopard," an upgrade to Leopard, the current version of Mac OS X, during the show. He provided no further details about the features or release date, focusing instead on the new iPhone. He also officially announced iPhone 2.0, a new software platform for the smartphone. Stressing the use of the iPhone as an enterprise device, Jobs said the new platform will build in support for Microsoft Exchange, allowing enterprises to push email, contacts and calendars from Exchange server to the iPhone.

The iPhone 2.0 platform includes an SDK (software developer kit), with native APIs (application programming interfaces) for developers to write mobile applications for the iPhone. Using the SDK, developers can write applications for location-based services, like photoblogging or to connect friends over social networks. The SDK's rich-media layer provides resources for developing 3D games and writing programs for audio and video playback on the iPhone. The SDK also allows development of database and touch-based applications.

During the keynote, companies demonstrated applications for the new iPhone, including Typepad, which has written an application to allow photoblogging. MLB.com demonstrated an iPhone 2.0-based program that shows video highlights of Major League Baseball games. Using the SDK, Modality has created a medical application that provides students with image and text-based reference content on human anatomy.

The iPhone 2 platform will be available as a free download in July. Developers will be able to sell their third-party iPhone applications through Apple's online App Store, which will be accessible by users in 62 countries.

Users will be able to download iPhone applications under 10MB over cellular networks, by Wi-Fi or through iTunes. Applications over 10MB will be available only through Wi-Fi or iTunes. Users will also be able to distribute applications by syncing iPhones.

The software platform also adds full contacts search, a calculator, improved language support and parental controls to for data access to iPhones, Jobs said.

"Some teenagers may not like this, but that's the way it is going to have to be," Jobs said.

The software platform will enable the entry of Simplified Chinese and Traditional Chinese and two forms of the Japanese language to iPhones. Users will also be able to view Microsoft Office (Word, Excel and PowerPoint) and Apple iWork (Pages, Numbers and Keynote) productivity documents on the iPhone.

Apple also announced MobileMe, a service to push email and synchronise information wirelessly on the fly. Storing information on a "pod," MobileMe immediately pushes updated email, contacts and calendars to devices, including cell phones and laptops. Users will be able to use the service on cell phones or through the website at Me.com. Users will also be able to transfer and share images and other documents. MobileMe replaces Apple's .Mac online service. Users using .Mac will be automatically upgraded to MobileMe, Apple said.