Rajabi also lauded iAd. "It seems quite robust, and I can see an entire ecosystem being developed around that platform," he said.

Version 4 offers an iBook reader as well and a developer preview of a game center.

The timeline for iPhone OS 4 has it available for iPhone 3G S and third-generation iPod Touch units this summer with all features supported. Users also can run the OS on iPhone 3G and second-generation iPod Touch, but some capabilities, such as multitasking, will not be supported. "The hardware just can't do it," Jobs said.

IPhone OS 4 ships for the iPad this fall.

Jobs  took time to tout the progress of iPad shipments. The notepad-based device began shipping this past Saturday. "So far, people seem to be loving it," Jobs said. On the first day of shipments, 300,000 iPads were sold, he said.