In a rollout of the OS Thursday at Apple headquarters in Cupertino, Calif., company CEO Steve Jobs heralded the release of a developer preview of iPhone OS 4.0 available . Users will be able to get the OS this summer.

Built for the , iPod Touch, and newly released devices, Apple highlighted seven "tentpole" features. These include iTunes-less corporate app distribution, additional enterprise security, multitasking, folders, an enhanced email client, iBook capabilities, games, and the iAd advertising platform.

"iPhone OS 4 delivers over 1,500 new APIs for developers, a lot stuff that developers have been asking for," Jobs said. He called version 4.0 "the next generation of the most advanced mobile operating system in the world."

Emphasizing the developer bent of Tuesday's unveiling, Jobs said that Apple has sold more than 50 million iPhones and that total iPhone and iPod Touch sales have reached 85 million. "If you're a software developer, that is a plum market to go after," said Jobs.