Sim Unlock your Blaze
Credit to: Owl74 and f_v_man and probably others too... See, http://forum.xda-developers.com/show....php?t=2024514
I have a T-Mo GS2 and Blaze, and have found that in many ways they are almost identical. I have previously flashed GS2 radios on the Blaze and vice versa. This process to Sim unlock worked on my GS2, so thought I would try it on my Blaze; it worked perfectly! My secondary sim from a non T-Mo provider is from TruPhone.
* Nandroid your current rom.
* Restore if you have it, or flash back to stock T-Mo ICS 4.0.4 rom (my stock rom is rooted btw).
* Flash the T989UVLE1 radio.
Radio thread: http://forum.xda-developers.com/show....php?t=1895400
Then follow these points from the cited thread:
Turn off phone. Insert a SIM from another provider into your phone.
Click "DISMISS" on the Enter Unlock Code screen after the phone starts up.
Wait a minute for the phone to power on and settle down.
Go to dialer screen. Press *#197328640#
The screen will change to the hidden menu as soon as you hit the last # key in the dialer:
Press DEBUG SCREEN
Press PHONE CONTROL
Press  SIMULATION
Press  NETWORK LOCK
Press  PERSO SHA256 OFF
Wait exactly 30 seconds
press the menu key on the phone and select back option. This will take you back to NETWORK LOCK screen.
Press  NW LOCK NV DATA INITIALLIZ
Wait exactly one minute and reboot the phone.
Your phone should now be Sim unlocked.
* Restore your previous rom's Nandroid (I went back to CM10 nightly)
* Flash a more current radio such as TLMC4
* You may have to reset or recreate an APN for your non T-Mo sim card.
Disclaimer: Use at your own risk, I'm just sharing. Also check out the original thread for questions and answers, as I may not be on the Blaze forum much - my Blaze is just a back-up phone now. Please hit Thanks if this helped.
Edit on Legality: Some say this is improper, others disagree. Regardless, I'll state this is just a hypothetical explanation...