Hope this will help

[batangnoda]

Got a second hand iphone 3GS fw3.0, bb4.26.08 ,, bl6.04.
1. Jail break with redsn0w 0.8 ... no problem
2. Install ultrasn0w (0.6, 0.8, 0.9, 0.92) not working on softbank but working on docomo
3. Upgrade to 3.1.2 but baseband still on 4.26.08. Used activated 3.1.2 spw from internet sources
4. Install ultrasn0w, the same trials with no.2, work on softbank for few hours then signal suddenly failed. Insert Docomo sim, signal was full bar
5. Visit softbank shop tried to buy official sim for iphone ( softbank is the official carrier of apple in Japan). after checking some details of iphone, softbank found out that the unit is block due to some unpaid bills of previous owner.

This might be the reason why no matter how i tried to unlock the iphone, it will not work on softbank. I know Iam not alone with this situation, try to go to the official carrier of your phone and know if your phone is in the same problem with mine.

Hope this will help others.

[mavrik101]

Makes sense, since the carriers can "see" the imei. Probably blocked it in their system.

[PWNsyst3m]

That sucks man.