Did your friend install modified software on that iPhone? Trying to restore a jailbroken phone can lead to the behavior you described.
I don't know exactly, but I think it's a possibility. I am trying to restore also with another Imac of mine, but with no luck, it report error 2001 or 1604.
Honestly i don't care about having the JB, there are any chances that i can restore the iphone with standard un-modified OS?
Edit: Now it seems it's stuck on a sort of Recovery mode loop. The diplay show the USB cable under the Itunes logo and Itunes warn me that the device need to be recovered in order to use. The recovery process fail and the iphone display turns black and itunes reports error 2001. Immediately after this the device enter again in recovery mode (USB cable and Itunes logo) and again Itunes ask for restore. Tried the restore twice always error 2001.
Try these suggestions, if they don't work and the phone has been jailbroken before, you're stuck because of the jailbreak.
Error 1604: This error is often related to USB timing. Try changing USB ports, uninstalling and reinstalling USB ports, and other available USB troubleshooting steps (troubleshooting USB connections, device not recognized properly, computer won't recognize a FireWire or USB device). If you are using a dock, bypass it and connect directly to the white Apple USB dock connector cable. If the issue persists on a known-good computer, the device may need service.
If the issue is not resolved by USB isolation troubleshooting, and another computer is not available, try these steps to resolve the issue:
- Connect the device to iTunes, confirm that the device is in Recovery Mode. If it's not in Recovery Mode, put it into Recovery Mode.
- Restore and wait for error 1604.
- When prompted, click OK.
- Close and reopen iTunes while iPhone remains connected.
- iPhone should now be recognized in Recovery Mode again.
- Try to restore again.
If the steps above do not resolve the issue, try restoring using a known-good USB cable, computer, and network connection.
Error 1611: This error may indicate a hardware issue with your device. Follow the steps in this article. Also attempt to restore while connected with a known-good 30-pin Dock Connector cable, computer, and network to isolate this issue to the device. The MAC address being missing or the IMEI being the default value (00 499901 064000 0) can also confirm a hardware issue. Out-of-date or incorrectly configured proxy or security software, such as FoxyProxy, can cause error 1611. To troubleshoot third-party security software, follow these steps.
Error 1639: See this article for resolution.
Error 2000-2009 (2001, 2002, 2005, 2006, 2009, and so on): If you experience this issue on a Mac, disconnect third-party devices, hubs, spare cables, displays, reset the SMC, and then try to restore. If you are using a Windows computer, remove all USB devices and spare cables other than your keyboard, mouse, and the device, restart the computer, and try to restore. If that does not resolve the issue, try the USB issue-resolution steps and articles listed for Error 1604 above. If the issue persists, it may be related to conflicting security software.