Here is a warning for those of who have downloaded iOS Beta 3. It was released this past Monday.
And hackers claim that its life will be short. According to iOS hacker iH8sn0w, this latest version of Apple’s mobile Operating System (OS) is set to expire on 30 September 2012.
What will happen after that? Nobody knows.
If you have not updated to iOS 6 beta 4 or maybe the official release of iOS 6 by then, your iDevice will be temporarily bricked. It will remain bricked until you update to either the official iOS 6, or a later beta version, whatever will be available at the time.
You should make sure to update to iOS 6 beta 4 when/if available, or to the official iOS 6 public release when it is available if you do not want to risk being locked out of your device.
It would not be the end of the world, but you would have to download the full beta software to your computer and go through the restore process. This would be much less convenient than a simple Over The Air (OTA) update.
Source: iDownload Blog