How do I update iPhone 3GS iOS 3.1.3 to 4.2.1?
My MacBook Pro runs on Leopard 10.5; my iTunes is version 10.6. When I attempt to restore the update in iTunes I get, "The iPhone could not be restored. This device isn't eligible for the requested build". The impression I'm getting is that Apple has locked out the possibility of upgrading to anything but the latest version (iOS 5.0). Long story short, I can't do that to achieve connectivity with my new car's media center. I need 4.2.1 for my 3GS. Any thoughts?
iPhone 3GS, iOS 3.1.3