Chosen Solution
My IPhone 3G 8GB has been unused for some months so when I switched it on it said a message to connect it to iTunes.When I did plug into my laptop however it shown the message below “The IPhone “iPhone” could not be restored. An unknown error occurred (1015)”.It is an unfortunate circle which has been repeated many of times and I was wondering if there could be something else for me to try. I have tried to troubleshoot the problem with the apple specific update-and-restore error messages and advanced troubleshooting webpage, however, when I find the correct number it redirects to the same page.
It sounds like it was jailbroken earlier which may be why your getting the error. Try putting it into DFU mode then trying the restore. If that doesn’t work there are some in depth using sn0wbreeze and the ISPW of the iphone.