Downgrade iPhone on Firmware OS 3.0 to Older 2.2.1 in Device Firmware Upgrade (DFU) Recovery Mode

Although the new iPhone OS firmware 3.0 is much better in almost every aspects with important new features, however, some may regrets upgrading their orginal iPhone 2G or iPhone 3G to OS software 3.0. One major complaint is that it’s harder to jailbreak or unlock iPhone firmware OS version 3.0. Beside, during the beta, iPhone UUID must be registered with Apple to update to beta firmware.

Luckily, it’s easy to downgrade from firmware 3.0, in procedure similar to downgrade from iPhone OS 1.1.1 to older version OS. When downgrading from iPhone 3.0, do not that only OS software can be downgraded, but not baseband 04.20.01.
1. Download iPhone OS software 2.2.1 .ipsw restore image.
2. Connect iPhone to Mac OS X or Windows PC system.
3. Run iTunes.
4. Select the iPhone from the list of devices in iTunes.
5. For some iPhone that does not been recognized by iTunes, or returns error message such as 1601, 1602 or 1600, the phone has to be put into DFU (Device Firmware Upgrade) recovery mode by following steps:
1. Connect iPhone to computer.
2. Turn iPhone off.
3. Press and hold Power and Home buttons on iPhone simultaneously for 10 seconds until phone turns off (screen goes dark) to reboot iPhone.
4. Right after iPhone reboots, release Power button but keep pressing Home button for about another 10 seconds, until the PC computers beeps or displays a notification as a USB device is recognized.
5. iTunes should automatically detect iPhone in DFU recovery mode.
6. On the Summary tab, press and hold Option (for Mac OS X system) or Shift (for Windows system), and then click Restore.
7. Browse and locate the iPhone firmware OS software update .ipsw file that was downloaded.
8. Click on Restore.
9. Ignore error message like 1011, 1013, 1015 that appears at the end of the restoration process even though the older version of the firmware OS software is successfully installed.

To jailbreak iPhone OS 2.2.1, use QuickPwn 2.2.5 or PwnageTool 2.2.5. To unlock iPhone, you probably have to downgrade to iPhone OS software 2.2 and uses yellowsn0w to unlock it.