AT&T 官方解锁iPhone 4 (无需升级最新操作系统) 操作步骤

从我本人的英文博客转载过来的，适合于使用美国AT&T 2年合约iPhone，并且合约期满官方解锁的朋友参考。特别是一般在AT&T客服联系苹果公司官方解锁后会要求你把iPhone链接iTunes
restore，然后iTunes会要求你升级到你升级到最新操作系统，而这可能并不是你要想到的。本文最后提供的几个步骤可以帮你绕开“升级”这一步。

I got my iPhone 4 with AT&T's 2-year contract in 2010, and recently upgraded my line to
iPhone 5. This way the iPhone 4 is off-contract and qualifies AT&T's unlock eligibility.

Unlocking an iPhone allows you to use SIM cards from local wireless carrier
when travelling aboard, which are usually cheaper than paying for international coverage from AT&T. You can also use the phone on other GSM carrier (CDMA in Verizon's case) in the United States, such as T-Mobile, although data speeds might be slower. If you
want to sell used iPhone on eBay or craiglist.com, unlocked phones are usually more popular.

After I decided to unlock my iPhone 4, I looked up online and here's
my procedures.

1. Look up iPhone's IMEI number

Go to Settings, then General, then About, write down the IMEI number.

2. Call AT&T customer service

Customer representative will verify your information and check unlock
eligibility. In my case, it only took less than 1 minute before the representative told me she had unlocked my iPhone through Apple.

At this moment, she told me to plug iPhone into computer and connect
to iTunes, do a backup, then click restore. The restore process will trigger the unlock.

So I plugged my phone, did a backup, and hesitated when trying to restore,
because it says my iPhone 4 will be restored to latest iOS version which is iOS 6. Considering there's no siri with iPhone 4, there really isn't much features to get from iOS 6. Then I wonder if there's a way to unlock iPhone without restoring and looked up
online again. Luckily got to this post.

I would like to endorse those steps here and add a couple of screenshots
that were captured in my unlock process.

1. Download latest version of redsn0w software at here

2. Run redsn0w on your computer





3. Connect iPhone to computer. Step 4 to 8 shows how to put iPhone on
DFU mode. iPhone is connected to computer during the whole process.

4. Turn off the device.

5. Hold the power button for 3 seconds.

6. Hold the home button without releasing power button for 10 seconds.

7. Release the power button but keep holding the home button.

8. Keep holding the home button until you are alerted by iTunes saying
that it has detected a device in Recovery mode. Make sure the device screen is blank and no logos (including Apple logo) are present.

9. When redsn0w recognized your iPhone in DFU mode. Choose Jailbreak.

10. Options will appear with checkboxes. Make sure the only box checked
is Deactivate then
click next.

11. Keep iPhone connected with computer. iPhone will flash words on the
screen then reboot.

12. After the iPhone rebooted, open iTunes on computer.

At this moment, you should receive a message in iTunes confirming that
your iPhone is officially unlocked.