The original release of RedSn0w to downgrade iPhone 3GS devices on the 06.15 baseband was unsuccessful for some devices.
After day of debugging why reverted 3GS had no service, found it was blocked for unrelated reason! OTOH I figured out how to change IMEI
Other than that testing hiccup, the revised payload seems fine...will release improved downgrade later today. Happy 4th of July!
You can find instructions on how to perform the baseband downgrade here: Windows, Mac.
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