To go along with the new iPhone, Apple announced that it is renaming the upcoming iPhone OS 4 to iOS 4. There will be roughly 1,500 new features included in iOS 4 along with multitasking, a unified inbox, app folders, and data detectors. Apple is encouraging all its developers to work with the iPhone 4's new high resolution display though iOS 4 will automatically redraw the text and controls for the older iDevices to display correctly. Bing is now a supported search engine along with Google and Yahoo. Google is still the default though I do believe you can switch which one that is.
Apple said that iOS 4 will be launch on June 21st for the iPhone 3G, 3GS, and iPod Touch. Owners of the Touch will also get the new OS for free which is a first for them. Not all features will be supported across the devices however, with owners of the first generation iPod Touch being left out entirely and the iPhone 3G not supporting multitasking.