Step 1: Close iTunes or any other application.
Step 2: Launch Tiny Umbrella then connect your iPhone 4 (Download Tiny Umbrella)
Step 3: Hit the “Start TSS” Server button
Step 4: Now launch iTunes and restore to iOS 4.1, (Note: do “Restore” not “Update“).
Step 5: Wait for iTunes to end up with “error 1004″. This is normal and has to do with the baseband not being updated.
Step 6: Simply “Kick Device Out of Recovery“.
That’s it. You’ve upgraded your iPhone 4 to iOS 4.1 with 1.59.00 baseband. [via ihackintosh]
