Please Note: This ONLY Works with the iPhone 4!
Download TinyUmbrella from here Also make sure to download the iPhone 4 iOS 4.1 Firmware located here
Double click the downloaded Umbrella.dmg file to mount it. Drag the Umbrella app from the mounted dmg into your Applications folder. Then double click the Umbrella app to launch it.
If asked enter your administrative username and password.
Make sure the device is connected, and Umbrella has detected the type of device and its firmware.
**If you haven't already saved your SHSH blobs then click Save My SHSH.
Hit Start TSS Server and make sure you receive no errors.
Once The TSS Server is "running" successfully, umbrella will kill iTunes. Leave TinyUmbrella Open.
If you do receive an error, DO NOT continue. Your restore will not work if the TSS server cannot be started.
Open iTunes and Hit Shift+ Restore.
Browse to and select the iPhone 4.1 Firmware File.
Hit OK to Restore iPhone
iTunes should give you error 1004. This is what we wanted, as it notes the baseband has not updated :)
Go back to the TinyUmbrella window and Click Kick Device Out of Recovery
*If you have issues here, try closing and re-opening TinyUmbrella.
Your iPhone will now be on 4.1 with the 1.59.00 baseband! (Which means you can now unlock using this tutorial)
**Thanks to semaphore for his work on this tool