The following is a guide to unlock the T-Mobile Samsung Galaxy S II with Z3X box. I have verified the steps below on Android 2.3.6 (not rooted) and it worked for me. It's not easy to get it right because of lack of information available elsewhere.
- Connect Z3X box to PC via USB
- Dial *#7284# on the phone, choose Modem for USB
- Dial *#9090# on the phone, choose USB Diag and then reboot the phone
- Connect T-Mobile Samsung Galaxy S 2 T989 to PC via a different USB port.
- Select model T989 in samsung tool 12.1.
- Click read info. There may be up to 3 more serial ports show up in the list in Samsung Tool
- Try select one of the serial port and then click unlock. If it does not work, try the next one. One of them should work
- If you see "Reading Security... Error Access Denied" when attempting to unlock, try a different serial port. If none of the serial ports work, try root the t-mobile Galaxy S2 Hercules phone with this guide
- Congratulations, now you have just unlocked your T-Mobile Samsung Galaxy S2!
To verify whether it's unlocked or not, just pop in a sim card from another carrier (for example, AT&T), 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. I managed to unlock it on both rooted and unrooted phones
- It works on 2.3.6 Android. I have not tried other versions.
- It works on Samsung Tool 12.1. Samsung tool 12.2 may have issues showing its unlocked but in fact it's not.
Does it work for you? Please leave a comment if this helped you unlock your phone.