I got this AT&T iPhone 5 purchased overseas for $800 plus tax.
As soon as I got it, I tried to restore it to bypass the activation screen required by AT&T. But restoring didn't go smooth as planned. Now the phone is stuck in recovery mode. And every time I place it in DFU mode, then restore with iTunes I get an error 21, if not in dfu mode 1603,1604, 1611 errors come out.
When restoring using DFU mode, what I notice is that iTunes has the loading label ‘preparing to restore iPhone’. The device on the other hand turns off, and comes up with the Apple logo and the daisy/spinning wheel. The wheel spins for about a quarter only and get stuck, and soon after reboots and goes back to Apple logo. After that is the popular iTunes and USB logo. Then, iTunes gives an "iPhone cannot be restored. An unknown error occurred (21)" something error. The process repeats every time I try to restore in DFU mode.
I've tried almost everything online relating to this issue: device off and hold home button while connecting the lightning connector and wait for the iTunes logo and USB to show up before releasing home button, for example. Done it for countless times, in 4 different computers.
I've tried it on 2 PCs with Windows 7 64-bit, a MacBook Pro and a Windows XP. The IPSW file I'm using is the 6.0.1 for GSM which is appropriate for my GSM device.
Been stuck for almost a week now, will be really sad if this is a hardware failure, it would mean additional expense for warranty.
Any other suggestions I should try for a fix? I really want to start using this device.