An earlier IBTimes UK report discussed AT&T's drive to unlock off-contract iPhones for US users and also those who purchased the phone in the US but later moved out of the country. However, the hitch with this carrier unlock process is that you lose all earlier jailbreak installations. In other words, AT&T's method involves backing-up and restoring your iPhone using iTunes, which actually wipes out all third-party installations including jailbreak.
What is the Best Solution?
The biggest question is - how do we unlock the phone without losing the jailbreak software? If any of you thought of using "Redsn0w", be warned it just does not work, according to JBU. The best option is to use a Subscriber Artificial Module (SAM) to bypass the IMEI security lock.
How Does SAM Work?
SAM is a creation of @sbingner which enables you to deactivate your iPhone 4S officially without needing a stock SIM. Those of you planning to incorporate jailbreak tweaks and features into your iPhones will need to jailbreak the device using GreenPois0n "Absinthe" posted here. The rest can skip the three steps and proceed to the end.
How to Unlock AT&T iPhone 4S Without Losing Jailbreak Using SAM:
Step 1: Head over to Cydia Store and add the source repo - http://repo.bingner.com - and select "Install SAM".
Step 2: Navigate to "Settings", select "SAM" then choose "Deactivate iPhone".
Step 3: First, SAM will deactivate your iPhone 4S. Then when you re-connect the iPhone to iTunes, it will officially re-activate the device.
Now you can activate your iPhone without using a stock SIM.
Meanwhile, those of you not using jailbroken devices can simply do this in one quick shot. All you have to do is tap "Reset all content and settings". If you have a locked iPhone 4 or 3GS, proceed to the step by step guide on how to unlock AT&T iPhone 4/3GS without losing jailbreak using "Redsn0w".