I have an iPhone 3G which I foolishly upgraded to iOS4 to try it out however whenever I try to restore my phone to 3.1.3 via xCode it says that there was an error downgrading the Baseband, and then enters recovery mode requiring me to restore it back to 4 before being able to use it again. I really need to go back to an earlier version to see if having version 4 on a 3G is causing my slow down problems, is this even possible?
Unfortunately, no. Apple digitally signs every install of iOS, and when iOS4 was released they stopped signing older versions. The only way you can downgrade is if you had captured your device's signature by using an independent server before upgrading.
That's a shame, will I be able to do it through less official means like the one explained here? Edit - If anyone is interested, the article linked above worked perfectly.