I am trying to fix an iPhone 4 for a friend, who bought it on eBay so we don't know how it got into this state, although my searches suggest that it may be the result of a jailbreak. My searches all seem to lead me down the route of putting the phone into pwned DFU mode and then restore in iTunes from there. I have used both redsn0w and iReb to put the phone into pwned DFU mode and then restore from iTunes but after some progress it always fails with the 1600 error. I have also tried to apply a jailbreak to the phone, but with absinthe it simply doesnt recognise the phone in DFU mode. It gets a bit further with redsn0w but nothing happens after the "waiting for reboot" message... Any help welcome!