I created this using pwnage tool unlock edition from the iPhone Dev Team.
This is a custom made ipsw 4.1 for iPhone 3gs with baseband 6.15 (ipad baseband.)
WARNING TRY AT YOUR OWN RISK- I have not tested it yet so please tell me if there is an error. I will also help you fix it.
ALSO READ WARNINGS IN THIS PAGE BEFORE DOING ANYTHING- http://blog.iphone-dev.org/post/1718400992/ultra-recycle
To Install You need to go to dfu mode and on windows press shift and restore, point to location of file and wait.
I have made them into .7z files so please get winrar or 7-Zip
I will try to upload in other sites were I do not have to pay, later.
Links-Mediafire