iPhone OS 4

Apple unveiled plans for the biggest and most exciting iPhone software update yet. iPhone OS 4 will include over 100 new user features for iPhone and iPod touch owners to enjoy. And for developers, a new software development kit (SDK) offers over 1500 new APIs to create apps that are even more powerful, innovative, and amazing.
The main weakness of the iPhone OS as long as this is going to disappear in version 4.0 that is multitasking capabilities and add many new features that make users feel at home and adds iPhone, iPhone attractiveness for potential new customers.
iPhone OS 4 will ship this summer for iPhone and iPod touch, and for iPad in the fall. A developer beta is available now
100+ New User Features
With iPhone OS 4, iPhone owners will enjoy over 100 new features that make it easier to interact with apps, manage email, read books, and more. New features include the following:
Folders
Organize apps into folders with drag-and-drop simplicity. Get faster access to your favorites and browse and manage up to 2160 apps at once — many more than the current limit of 180 apps.
iBooks
The best way to browse, buy, and read books on a mobile device. Easily flip through the pages of a book you've downloaded from the iBookstore while listening to your music collection. Browse tens of thousands of books — many of them free — by title, author, or genre. You can even check out reviews and read sample pages before you buy
Multitasking
Developers will have access to seven multitasking services, which will allow tasks to be performed in the background while preserving performance and battery life. So you’ll be able to make a Voice over IP call while playing a game or checking email, find a restaurant on Urbanspoon while listening to Pandora, and more.
Even Better Mail
See messages from all your email accounts displayed together in a unified inbox, switch between inboxes more quickly, organize messages by threads, and even open attachments in third-party apps
iAd
iAd is a breakthrough mobile advertising platform from Apple. With it, apps can feature rich media ads that combine the emotion of TV with the interactivity of the web. For developers, it means a new, easy-to-implement source of revenue. For advertisers, it creates a new media outlet that offers consumers highly targeted information
iPhone OS 4 Compatibility
iPhone OS 4 will work with iPhone 3G, iPhone 3GS, and the second- and third-generation iPod touch this summer, and with iPad in the fall. Not all features are compatible with all devices. For example, multitasking is available only with iPhone 3GS and the third-generation iPod touch (32GB and 64GB models from late 2009).


adapted from : http://aplle.com/