Samsung Galaxy S II / SGH-T989
To unlock the device, you need to be using the UVLE1 radio. This is used with an Android 4.0 ROM.
The Android 4.0 ROM I used was called "TechNiqCality" (do a search for "TechNiqCality_3.0.zip").
I first found the information on XDA: http://forum.xda-developers.com/showthread.php?t=2024514
Once you unlock with UVLE1 / Android 4.0, you can then flash anything else (the current CyanogenMod, stock Samsung 4.1.2, etc). The unlock should remain permanent.
TWRP Recoveries:
(flashable via CWM or TWRP)
2014/03/07:
twrp_2.7.0.0_hercules.zip (8,607,783 bytes)
CWM Recoveries:
(flashable via CWM or TWRP)
cwm-6043-hercules.zip (7,960,922 bytes)
Custom Binary Download counter reset:
(flashable via CWM or TWRP)
sgh-t989-flash_counter_reset.zip (181,291 bytes)
SGH-T989 Radios
(flashable via CWM or TWRP)
UVLE1 (Android 4.0)
sgh-t989_uvle1_radio.zip (20,704,600 bytes)
UVMC6 (Android 4.1+)
sgh-t989_uvmc6_radio.zip (20,825,694 bytes)