AT & T now allows you to unlock your iPhone so that you can use it on other service provider or carry it overseas. The unlocking process requires to update phone firmware through iTunes, which breaks your iPhone Jailbreak. Don’t worry, there is an easy way to unlock your iPhone without loosing the Jailbreak
Step 1. Initiate the unlocking process by chatting with AT & T customer service. With in few hour you will get an email with the steps required to unlock your phone.
Step 2. Download and launch the latest version of redn0w (Windows or Mac) and select the jailbreak option.
Step 3. When asked to install Cydia, uncheck the option and check the box marked with option Deactivate.
Step 4. Now connect your phone to iTunes and it will activate with the new unlock and the jailbreak.
This process works on all iPhones except iPhone 4S.