Recently, the iPhone OS 4.0 Beta was released and tested out by many developers and users. If you’re not happy with the new OS 4.0 or find it unusable, then here is a tutorial by MuscleNerd (from iPhone Dev team) which can let you get back/ restore the official iPhone OS 3.0 firmware.
Follow the steps below carefully to downgrade –
Restore to official 3.1.2 or 3.1.3 using iTunes. Your baseband won’t be downgraded, so you’ll get error 1015 at the end of the restore.
Use rslite or irecovery to get past error 1015. Using rslite, you’d do:
% rslite rslite v0.2 - by the iPhone Dev Team, 2009. --THIS IS AN UNSUPPORTED TOOL-- Connecting... [Recovery] setenv auto-boot true [Recovery] saveenv [Recovery] reboot
Wait a few seconds, disconnect the iPhone from cable, then reboot the iPhone.
The Apple logo will appear on the display as you connect the phone via USB cable and proceed with the activation.
Your iPhone should be downgraded from iPhone OS 4.0 to iPhone OS 3.1.2 or 3.1.3
Note – Your baseband will still be at 05.13 from the stock 4.0beta1, but FW 3.1.2 and 3.1.3 will work fine with it. The current carrier unlocks will not.
Disclaimer: This article is for testing & informational purposes only. Try at your own risk!