Downgrade the baseband 06.15.00 to 05.13.04

It's finally available iPad Downgrade baseband 6.15.00 on the iPhone 3G and 3G. Now you can fix problems with GPS and even upgrade to any official firmware.

NOTES:

• It comes down to the baseband 05.13.04 which is releasable with Ultrasn0w
• You can install the 6.15.00 baseband and then downgrading to 05.13.04
• It does not work for iPhone 3G with serial number after XX134XXXXXXX (if you do your iPhone will stop working)

TUTORIAL:

NEED:

RedSn0w 0.9.14b1:

• Mac
• Windows

The IOS has your device now. Download it here.

STEPS:

Open Redsn0w

Click Extras

Click Select IPSW

Select the firmware of your device, you've downloaded, the same as you currently have.

Whether your iPhone 3G is old or new bootrom

Return to main menu and click Jailbreak

Downgrade from iPhone baseband Select and deselect all others if you already have Cydia installed.

Connect your iPhone and turn it off

Click Next

Put your iPhone in DFU:

Press the Power button for 3 seconds

Without releasing Power, press Home and keep both pressed 10 seconds

Drops Home Power and hold for 10-15 seconds.

Your iPhone will reboot and start the process at the point Flashing Baseband can take up to 10 minutes, do not cancel or disconnect for any reason.

Once finished restart with the new baseband, go to Cydia and install Ultrasn0w

NOTE:

If you finish your baseband is still 6.15.00 redo the whole process.

Source - iClarified