the phone was purchased from second hand shop here in Japan. It was originally from softbank.
it was on 3.0 Fw, 4.26.08 modem fw, and 6.4 bootloader,

1. successfully jailbreak with redsnow 0.8 but unable to unlock with 0.92 ultrasn0w
2. upgrade to 3.1.2 without changing its modem fw. ( used activated 3.1.2 ipsw from internet sources)
3. Install ultrasn0w 0.92 then insert softbank sim, it worked for several hours then signal failed. Now even the carriers name ( softbank)is not present on the signal bar area
4. Inserted Docomo sim, its working the docomo name is present and the signal bar is full.
5. Tried to replace docomo sim with softbank sim ,,,, no signal, no carriers name its just a flat bar.Tried to look for the phone number of sim on phone setting, the number is there

Any idea what wrong with this