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.
- Connect AT&T Samsung Galaxy S 2 Skyrocket 4G to Z3X box with the RJ45 C3300K cable
- Dial *#7284# on the phone and select modem for USB
- Dial *#9090# and select USB (1)
- Reboot the phone
- 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.
- 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.
- 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.