You have to know that updating your firmware to iOS 5.1.1 will update your baseband the reason that will let you not able to use ultrasnow unlocking solution so we recommend to use to use the link posted here to preserve your baseband while upgrading to iOS 5.1.1.
Ultrasn0w 1.2.7 Supported Basebands:
Unlock iPhone 4, 3GS On 5.1.1 With Ultrasn0w 1.2.7 :
Step 1: Jailbreak your iPhone on iOS 5.1.1 using the links below:
Step 2: After jailbreaking your device Launch the Cydia application then select “Manage” –> “Sources” then “Add” and Write down the link below:
Step 3: Open the added repo (Step 2) you will find ultrasn0w tap on it and press install then Confirm at the right corner to install ultrasn0w 1.2.7 to unlock iOS 5.1.1 on iPhone 4, 3GS.
How to Factory Unlock iPhone 4 – 3GS iOS 5.1.1 Using MEI Unlock:
Step 1: Go to MyIMEIUnlock.com
Step 2: Go to iPhone IMEI Permanent Unlock page.
Step 3: Check Your Country and Network
Step: 4: Place an Order
Step 5: Wait for Confirmation Email.
Step 6 : Connect your iPhone to iTunes [ Congratulation Your iPhone has been Unlocked]
Why My IMEI Unlock.com :
1- Read what Their Testimonials Says ?
2- What is Google Shop Rate For them [ See Here ]