iPhone 4 with iOS 4.x
and some tool to access the iPhones filesystem; iExplorer, iPhoneBrowser, ..
Download iOS 5.0.1 for your device:
First we create a custom firmware with the PwnageTool.
Start PwnageTool and select Export Mode. Choose the iPhone and
When asked save the custom firmware to your desktop.
Connect the iPhone via USB and follow the instructions to enter the DFU mode.
Open iTunes and click on "Restore" holding the "alt" key.
Select the custom firmware from your desktop and wait till your iPhone is updated and the back (i hope you made one before we started) is restored.
Now access the iPhone filesystem and place the fmod.deb in the directory:
/var/root/Media/Cydia/AutoInstall/Your might have to create the Folders Cydia/AutoInstall in case they dont already exist.
This is the cydia auto installation directory and every .deb you place inside will be installed on the next reboot. Which we do next, after a few seconds you should have a working SIM in your carrier locked iPhone 4. Enjoy!