If you’re the excitable type, you may want to try the iOS 4.0 Gold Master right now. This is probably the most dangerous thing you can do to your phone aside from run over it with a car, so don’t say we didn’t warn you. There are many sources, obviously, so do a Google search.
WARNING: If you’re running an unlocked iPhone, turn back now. This is not ready for you. If you’re willing to risk a good bricking or a failure to unlock, then go ahead.
1. First, download the iOS 4.0 GM from your favorite source. It should be called something like iPhone2,1_4.0_8A293_Restore. Don’t double-click it. It should be an ipsw file.
2. Next, find iTunes 9.2 beta from your favorite source. Install it. It is Mac-only right now, but expect a Windows version soon.
3. Prepare to restore to the new firmware.
Mac users: Click on restore while holding down the option key.
PC users: Click on Restore while holding down the shift key.
4. Watch the update and activation for problems. Again, this is a dangerous process fraught with peril. Feel free to try it and you can downgrade back again if you like using these instructions.