For more detail about Redsn0w (Redsn0w 0.9.14b2) is making you able to downgrade iPhone 3GS or 3G with iPad baseband 06.15.00 to 05.13.04 baseband, as the result you can enjoy the GPS and Ultrasn0w unlock for your device.
In 0.9.14b2 version, the baseband downgrade activity is improved to respond the older version of Redsn0w that is reported doesn't have a couple of NOR chips support. And this update gives 3 various models of NOR chips in both iPhone 3GS and iPhone 3G.
Therefore if you are an iPhone 3GS owner who is unable to downgrade 06.15.00 baseband back to 05.13.04 baseband, then Redsn0w 0.9.14b2 can solve your current problem.
As I mentioned in the first paragraph, aside of the baseband downgrade improvement, DFU IPSW also included in order to assists iPhone with broken buttons to put their iOS device into DFU mode. And the feature can be getting through: Extras –> Even More -> DFU IPSW.
If you are interested you can used the below links to download this version based on your existing operating systems.
Download Redsn0w 0.9.14b2 for Mac OS X and Windows.
Go to this page learn on how to downgrade iPhone 3GS and iPhone 3G 06.15.00 baseband to 05.13.04 baseband With Redsn0w.