According to a sources inside the Cupertino's iPhone software development effort, it is "highly probable" that the iPhone 2.0 Golden Master will be done this Friday. The final version could arrive to developer hands two weeks before the introduction of the new iPhone 3G and well in time for the promised July 11 release to the public. Update: for some reason, this morning I saw the original "end of June" release date and copy and pasted that as the release date link, rather than the obvious July 11. My apologies. J.
The iPhone 2.0 operating system Golden Master will follow the release of build 345, which has seen the activation of two code-signing and encryption features not previously available.
Keep in mind that this date is tentative, even if the source remarked that "this is the plan." Meanwhile, the iPhone Dev Team has confirmed they are working hard cracking the latest build, getting ready for the pwnage of the final release. Also, remember that releasing a Golden Master internally or to developers doesn't mean releasing it to the general public. As announced publicly during WWDC, Apple will make the update available in July.