Apple has released the developer version of iPhone OS 4, which allows developers to understand the new features included in the OS. This beta version is only available for developers who have the developer’s account.
You can get the developer’s account by paying $100 to Apple, but some people can’t pay this amount due to several reasons. iH8sn0w, a popular hacker, has the solution of the problem.
He has posted a video on Twitter, which shows a trick to activate latest iPhone OS 4 beta on your iPhone or iPod Touch.
As displayed in above video, you just need to remove following two lines of code from SystemVersion.plist file.
<key>ReleaseType</key>
<string>Beta</string>
Please note that I have not tried this technique to install the iPhone OS 4 beta. It may or may not work on your device. Also, if you upgrade to iPhone OS 4, your device will get updated to new baseband i.e. 05.13.03 and you will permanently lose the unlock.