Knowing

Are you planning of upgrading iOS on your iPhone 3gs or 4g ?
And are you scared to loose your unlock?
Or if you have upgraded your 3gs to 6.0 and dont no now how to unlock it ?

Then, Lets get through this process.

Jailbreak iPhone 3gs/4

• Download the latest version of redsn0w .
• Download official iOS 6 IPSW for iPhone 4 (GSM) or iPhone 3GS directly from Apple.
  
• Launch redsn0w and go to Extras > Custom IPSW.
• Point to the IPSW you just downloaded in Step 2. If you have a 3GS, you will be prompted whether you have a 3GS with old or new bootrom. Select appropriately.
• Redsn0w will start building custom iOS 6 while removing the files that will update your baseband. Once completed, you will find this file on the same file path as the original IPSW with the prefix “NO_BB…” followed by the IPSW file name.
• Be sure to pwn DFU your iPhone with redsn0w by going to Extras > Pwned DFU. Simply follow the on-screen instructions.
• Once your iPhone is in DFU, launch iTunes and press Shift+Restore (Windows) or Option+Restore (Mac). Be careful not to select the wrong IPSW during restore!If you get error 3194, you need to edit your hosts file. See here.
• Wait for it to finish. Your iPhone will attempt to reboot and may stuck on the Apple logo with empty progress bar due to tethered jailbreak.
• Launch redsn0w again > Extras > Just Boot. Follow on screen instructions.
• Your iPhone will boot up normally and is activated .If not activated you can activate through redsn0w through jailbreak button and then again repeat tether process.

Unlock iPhone 3gs/4
[Note :Notice that iPhone must be activated to unlock either with ultrasn0w or with Gevey sim.]

Unlock iPhone 3gs/4 through ultrasn0w

-Also Notice only these iPhone with these baseband could be unlocked for now with ultrasn0w.

• 01.59.00 (iPhone 4)
• 04.26.08 (iPhone 3GS)
• 05.11.07 (iPhone 3GS)
• 05.12.01 (iPhone 3GS)
• 05.13.04 (iPhone 3GS)
• 06.15.00 (iPhone 3GS)

To unlock with ultrasn0w. Follow below procedure:-

• Launch Cydia through iPhone home-screen and add the following repo by going to Manage > Sources > Edit > Add:Untitled Document
• 2. Let it update sources and packages and then search for ultrasn0w fixer for iOS 6 and install it.
• 3. Finally, search for ultrasn0w (1.2.7) and install that too.(If you didnt found it then on cydia,add repo by going to manage>sources>edit>Add: ultrasn0w.com )
• 4. Reboot your device.
• You should get a signal bars now !!!

Unlock iPhone 4 through Gevey Sim:[Note:: For iPhone 4 having baseband 2.10.04, 3.10.01, 4.10.01 you can just use Gevey sim and unlock it, no need to go through above unlock process just you can use gevey manual process after jailbreaking procedure.]