So finally the announcement of final version of iPhone OS 4.0 has been made at WWDC 2010 by Steve Jobs. iPhone OS 4.0 was first time announced back at Apple iPad preview event and till today four beta release of iPhone OS 4.0 has been made.
Another interesting part of iPhone OS 4.0 is, it has been renamed to iOS 4.0 hence from now onwards it will be called as iOS 4.0 for iPhone 3G/3GS and iPhone 4 (Next Gen iPhone i.e iPhone 4G). iOS 4.0 Golden Master Candidate is available for download to the developer registered for iPhone Developer programe.
iOS 4.0 will be free upgrade for iPhone 3G, 3GS & iPod Touch 2G & 3G excluding iPod Touch 1G. Also not all features will be available on iPhone 3G iOS 4.0. The iOS 4.0 will be available for everyone from June 21st.
Beware jailbreakers and unlocker, not to update to iOS 4.0 unless iPhone Dev Team announces or releases jailkbreaking & unlocking tools for iOS 4.0.