How to unlock Samsung Galaxy S II Skyrocket 4G I727 with Z3X box

The following is a guide to unlock the Samsung Galaxy S2 4G SkyRocket with Z3X box. I have verified the steps below on Android 2.3.5 (not rooted) and it worked for me. It's not easy to get it right because of lack of information available elsewhere. 

1. Connect AT&T Samsung Galaxy S 2 Skyrocket 4G to Z3X box with the RJ45 C3300K cable
2. Dial *#7284# on the phone and select modem for USB
3. Dial *#9090# and select USB (1)
4. Reboot the phone
5. There may be more than one diagnostic ports show up in Samsung Tool 12.1. So try them one by one. One of them will be able to readinfo and unlock. 
6. Congratulations, now you have just unlocked your AT&T Samsung Galaxy S2 4G Sky rocket !

To verify whether it's unlocked or not, just pop in a sim card from another carrier (for example, t-mobile), and reboot the phone. If the phone is not unlocked, it will prompt you for unlock code upon startup. 

Note:

• It does not require the phone to be rooted
• It works on 2.3.5 Android. I have not tried other versions.
• It works on Samsung Tool 12.1. Samsung tool 12.2, 12.3, 12.5 may have issues showing its unlocked but in fact it's not.
• If *#9090# code does not work then try the following: 1) power off the phone 2) connect microuart cable and power on the phone 3) now try *#9090# code again it must work 4) select USB diag and reboot the phone

 

Does it work for you? Please leave a comment if this helped you unlock your phone.