This is not mine info, but would this work for me to restore to 4.1 without baseband?
1.Download 4.1 IPSW for 3GS
2.Once downloaded, rightclick on IPSW file > Open with... > WinRAR.
3.Inside archive, delete file named 018-7073-079.dmg
4.Save the same file, DO NOT CREATE new one.
5.Open iTunes...