I figure people have probably moved on from this phone, and at some point so will I. My own experience with Android has not been pleasant (though this might just be a Samsung thing), and I plan to migrate back to Apple. Regardless, I still currently have an SCL21 and will be traveling this summer so I have been looking into SIM Unlocking this bastard. Below are my findings.
If you are still looking to unlock and have the resources (additional sim card) to try, I have combined some steps from two sources below. I have gone through the steps, but have not been able to verify b/c I lack an additional sim card and my buddy who has an iphone no long has his sim adapter. Once you set your band preference to GSM ALL, your mobile connection will disappear. This is normal. Please put in a GSM sim card (softbank perhaps?) and test it out.
The main steps are from HTCSOKU
(who incidentally puts out some pretty good all around info). In addition I have combined information from a Vietnamese site, this information was from unlocks of firmware 4.0.4. Regardless of which firmware version of you, please try this out and report back if this worked for you. You may have to modify steps here and there, though all settings are reversible.
It goes without saying that you full responsibility should you try this. There will be no hand holding. Use your common sense, go slow, make your own notes.
If you are on firmware 4.1.2, the following procedure will open the Service Menu for you.
1. Dial *#9090#
2. Press Menu > Back
3. Press Menu > Key Input
then type Q
(yes that is correct) and hit OK
4. Press Menu > Key Input
then type 0000
(that is four zeroes) and hit OK. Wait a couple of seconds and the Service Menu (DIAG CONFIG) will open up.
Unlocking steps are as follows.
1. Press UMTS > DEBUG SCREEN > PHONE CONTROL > NETWORK LOCK > PERSO SHA256 OFF
. Wait 30 sec, then hit Menu > Back until you see NETWORK CONTROL
at the bottom.
2. Press NETWORK CONTROL > GCF > GSM/(E)GPRS/WCDMA REL5
. Then hit Menu > Back until you see BAND SELECTION
3. Press BAND SELECTION > GSM > GSM ALL
4. Turn off your phone, put in a new SIM card and see if it worked.
If it doesn't work. Then repeat steps 2 & 3 above but change the selection to SETTING CANCELLATION
and DEFAULT BAND PREFERENCE
respectively. Turn off the phone, replace your original SIM card, boot and your LTE should be restored.
It should be noted that even if this does work, it will only allow you to use 3G since this phone only supports LTE BANDS 11 and 18. YMMV.