Apple lacks the systems and device management server applications offered for enterprise customers by Microsoft and Research in Motion. Through its support for Microsoft Enterprise ActiveSync, however, iPhone OS devices can make use of management and security features offered by Microsoft Exchange Server.

The new OS will also support , enable multiple Exchange accounts on a single phone and offer SSL VPN support via and Juniper.

Enterprise users will likely also appreciate another main new feature: the unified in-box. IPhone users can have multiple e-mail accounts, all showing up in one in-box. Version 4 will allow organization of e-mail threads with visual indicators; and you can open attachments with a fingertap.

The updated firmware will be available to all iPhones and iPod Touches, but only the latest models, the iPhone 3GS and third-generation iPod Touch, will have the hardware to support some of the more advanced features, such as multi-tasking. Users of the older devices can get the new software this summer and use many but not all of the new features.

Programmers can immediately access a "developer preview" of the new version at developer.apple.com.