iOS 5, the latest version of the world's most advanced mobile operating system, includeing over 200 new user features, and an updated SDK with over 1,500 new APIs and powerful new development tools- is now live! Developers can take advantage of iCloud Storage, Newsstand Kit, Core Image, GLKit, Twitter and new Game Center APIs.
iOS 5 features iMessage- a new messaging service that works between all iOS 5 users over Wi-Fi and 3G. iMessages are automatically pushed to all iOS 5 devices, making it easy to maintain one conversation across iPhone, iPad and iPod touch. In iOS 5 SDK, the Message sheet now supports the iMessage service, so you can start individual or group text conversations from within your app.
There are many more new features added, and the old ones upgraded. For more detailed information click here.