Its happy news for people who are stuck at the 06.15.00 baseband. The iPhone dev team has announced a baseband downgrade option for those iPhone 3G, 3GS users who are on the iPad baseband (06.15.00). The option is just a new add to the redsn0w tool.
With this new option, you could downgrade your iPhone to 05.13.04 baseband from the iPad baseband enabling you to use the GPS functionality plus getting an unlock with Ultrasn0w. The use of stock ipsw will also be supported once you downgrade your baseband.
You would have to just point at your firmware’s ipsw file using redsn0w and then go back, switch your iPhone off, click the Jailbreak option, check the box to downgrade iPad baseband and move along with the usual steps of Redsn0w.
The Redsn0w update is not yet out, but it is soon to be out in an hour as said by iPhone Dev Team member Musclenerd. But we will be reporting it within minutes of its release. Join us on Facebook or follow me on Twitter to stay along with our updates.