Very strange iPhone 3G issue please help!

[bellyfrog]

Hey,

I have this iPhone 3G which I just put onto 4.2.1 jailbroken. It is running 5.12.01 baseband. Everything went fine until I unlocked the phone and put the new SIM in... "No SIM Installed"... However when I put the AT&T sim back in it recognizes it straight away!

I've tried this with 2 different SIM cards and it won't recognize either of them, it only recognizes my AT&T sim card...

Does anyone have a clue what's going on and how to fix it?

Thanks

[i.Annie]

You're using the newest version of ultrasn0w? And you're sure your baseband is still at 5.12.01 and you didn't accidentally upgrade it?