After unlocking iPhone 3gs 4.3.1 with baseband 6.15 there is no signal

[Lathar]

I have gto iPhone 3gs 4.3.1 baseband 6.15, and I have unlocked it successfully with Ultrasn0w 1.2. But now the sim is not showing any signal. Can anyone tell me why is this happening? Help lease.

[Odalis]

If you have 4.3.1 just downgrade it to 4.1 and use TinyUmbrella and then Redsn0w to unlock the phone.Just follow the foll steps in order to downgrade:
1: Run iReb 4.0 applications designed to convert your device, that isn’t already jailbroken. Or else use Tiny umbrealla, this tool is very helpful for most users that jailbreak there iDevice. It puts your phone into DFU mode.
2: Once you have FDU, you can again install any firmware hen. Just install 4.1 and you can then perform Jailbreak via redsn0w 0.9.6b6
3. Once jailbreaked you can unlock it using Ultrasnow.

[Lathar]

Thanks for the help, I will try to install 4.1. But I don’t understand UDF, what is it? What is it used for? How will I know if my phone is in the UDF mode? Please explain it to me, before I try anything I am worried that I might brick the phone.

[Mayur_Jain]

DFU stands for Device Firmware Update which is a mode in which your phone is switched off, and there is no logo. You can get DFU by following method:
• Launch iTunes and connect the iPhone to your computer
• Turn off the switch off button and Hold down the iPhone.
• Hold down the sleep/power button and home button together for about 10 seconds, then just leave the sleep button.
To exit you just have to perform reverse method. Just the door is opened by moving both gates

[Lathar]

Thanks I solved the problem, I downgraded the iPhone. It gave me error 1015 though , that device is stuck in infinite loop and shut down. Then use this button to turn off the pc. You should kick from recovery mode.