Apple iPhone OS 4.0 will not be available to end-users before summer 2010, However, Apple has made available the beta build of the OS to developers registered with them - but for the adventurous users out there they can now download iPhone OS 4.0 Beta 1 as it is now leaked and posted on internet by iModZone.net.
But even if you download iPhone OS 4.0 Beta you still need to have your Device id registered with an dev Account and live up with an non-jailbroken phone as we don't have any working iPhone OS 4.0 jailbreak now, the good news is there is a un-confirmed way to get your device registered with an developer account as shown next.
You can download iPhone OS 4.0 Beta 1 for your iDevice from direct download links provided at - http://imodzone.net/download/, however you will need to have your device id's linked with an developer account to use them -
luckily somebody at iModZone forums has offered to do this and all you need to do is to email him at deleted for help.
I was contacted by the owner of the email id and here is what he has to say :
Would you please remove my email address from this link as I am not adding
one to a dev account and I am getting flooded with emails. :-) Thank you.