iLiberty has the option to download additional payloads from a repository on the developer's website.
In the windows version I downloaded the repository address that is pre-set in the application is old and does not work. The correct payload repository is
http://iliberty.insideiphone.com/repo.plist
Once you get this working, there are payloads to upgrade and downgrade your bootloader. You can go to 4.6 stock or to 3.9 with fakeblank.
Try 3.9 with fakeblank. Then try to flash your baseband again with 0.4.0.4.0.5_G
I think this is the same as the "fix for no signal, no wifi, no bluetooth" option which combines the two, so you might want to try that also.
Your problem is likely not that your baseband is empty (which is possible) but that your baseband bootloader is corrupted.
It is possible to permanently nuke your baseband bootloader and thus also your baseband, I hope this is not what you have already done. I strongly doubt it though.
Bricking your S-Gold [iPhone Dev Team]
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