I sorted out a mate with a 3g by running redsn0w and upgrading to 3.0.1.

All was working fine, but now he wanted to go to 3.1 (he doesnt use an unlock, but I advised using the custom ipsw).

Another friend with a mac made a working 3g ipsw... gave it to him... I got him to put the phone in DFU, then do a shift-restore...

It failed with error 1601, and now his phone is stuck in DFU... itunes says a phone in recovery mode detected, and the phone screen is blank.

How can he get this back working? restore to stock 3.0.1, and then what - redsn0w again, then reflash 3.1, or does he have to go to 3.1 properly and wait for a jailbreak?

Any advice most welcome... also what did we do wrong to get 1601 error?

Thanks

b0b808

Alright. Well, you can get out of DFU mode by pushing and holding the power and home buttons simultaneously for 10-15 seconds.
I don't remember exactly for how long but the iPhone should reboot in the end.

Now, since you have a friend with a Mac I would suggest using this machine to jailbreak 3.1.
The thing with iTunes errors 16xx is that somehow using a custom .ipsw with iTunes is only possible with an already jailbroken device or using PwnageTool to get into DFU mode.
I'm talking about iTunes 9 here.

So you guys got 3 options:

#1 - Using the Mac

Restore your device to stock 3.1 (since you're not relying on an unlock you might as well update the baseband).
Reboot your iPhone once. Go to '~/Library/iTunes/Device Support/' on the Mac and delete any files in there (don't worry, they're gonna get rebuild as needed). Reboot the Mac.
Fire up PwnageTool. You don't have to build another custom .ipsw if you already have one. Just click on the button 'DFU mode' and follow on screen instructions (somehow DFU mode with PwnageTool is different from just DFU mode). When you're successfully in DFU mode start up iTunes, but don't close PwnageTool! iTunes should detect an iPhone in maintenance mode. Dismiss the warning and close iTunes. Now close PwnageTool and then start up iTunes again. Just leave your iPhone plugged into USB all the time. Dismiss the warning again and this time alt-click Restore and choose your custom .ipsw. It should work without an error 16xx.

#2 - Using Windows

Since you can't use PwnageTool on Windows to get into 'special' DFU mode, you should restore to 3.0.1 and in turn use redsn0w to jailbreak.
Then with an already jailbroken device you should be able to use your custom .ipsw with iTunes without getting 16xx errors. You might not even need DFU mode then.
Just turn on your iPhone, hook it up to USB, start up iTunes, and shift-click restore to your custom .ipsw.
You might as well consider removing all files found in '%appdata%\Apple Computer\iTunes\Device Support\' beforehand and restart your PC just like you would do with the Mac.

#3 - Using older version of iTunes

Probably the most time-consuming option. You could try and downgrade iTunes 9 to an iTunes 8 version. I don't really know how to do that on Windows and even more important I don't know if it solves your 16xx errors. But you might as well try this if #1 and #2 don't work out for you.

Hope this helps for now...
Good luck!

cheers... put it back to 3.0, then redsn0w'd it then flashed with the custom ipsw without dfu

this time it worked, butnow he doesnt have visual voicemail? any idea why, or how to get it workign again? he is in the UK and using an iphone sim, and had it on 3.0 and 3.0.1

Glad it worked :-)
About visual voicemail... I think it has something to do with the new signed carrier bundles, since internet connection, MMS, visual voicemail, and tethering are all carrier specific settings. With 3.1 Apple started to sign carrier settings with an encrypted key. So depending on your carrier you have, for example, tethering activated or not.
I think the same applies for visual voicemail.
Your best bet would be to ask your carrier about it though, maybe it just needs to get reactivated.