It's not technically impossible but it's difficult. You need the IPSW file for the device/OS version and if it's old, you may also need the electronic signature as Apple only signs the most recent build. Even if you do get it to install, the baseband only goes one way so you'd be running an iOS 5 baseband with iOS 4.
It's really not recommended. On Oct 31, 2011, at 5:03 PM, Nathan Sims wrote: > How does one restore an iPhone running iOS 5 to a previous version, say > 4.3.5? iTunes only lets me reinstall iOS 5 again... _______________________________________________ iPhone-talk mailing list [email protected] http://www.omnigroup.com/mailman/listinfo/iphone-talk
