iOS 4 includes third party app multitasking support, the ability disable Location Services on an app-by-app basis, folder groups for organizing apps, a unified In Box in the Mail app so users can see messages from all of their email accounts at once, and message thread viewing. The new OS also includes support for Bluetooth keyboards, improved security, improved enterprise market features, and more.
Apple is also including support for Microsoft’s Bing search engine in iOS 4, along with Yahoo! and Google.
iOS 4 doesn’t support the first generation iPhone, and some features, such as multitasking, aren’t supported on the iPhone 3G.
The golden master version of iOS 4 is available to developers today, and will be publicly as a free upgrade for the iPhone 3G, iPhone 3GS and iPod touch on June 24.