By the way, it has concerned me that at least a couple of threads on discussions.apple.com have said that an iOS downgrade such as I described two blog posts ago is "
not possible". I feel that that's misinformation, and I don't know where it's coming from, but I don't like to end it on that note, simple to understand as it may be. This is because, while "no" is a simple answer, it's not (always?) the correct answer to this question. As my previous post states, I was able to downgrade.
You don't have to do anything illegal, or anything which will even void your warranty (because you're putting Apple-approved software on it). That said, even though I will give you a basic overview of the steps you'd need to take, I will not tell you how to get any of the individual steps done beyond what's simple to jot down here. Partially that's to avoid taking on your responsibility, partially that's because I don't want to keep writing forever. If you don't know how to do get a step I describe done, the responsibility to find out how falls on you, to research it. Search engines are your friend.
What you need:
I will say that you need to put some forethought into it. Specifically, you need to have kept a backup of your iOS 5.1.1 install file. It will be named something like "[model of your iOS device]_5.1.1_9B208_Restore.ipsw", and while 5.1.1 was the latest iOS you've used your computer to install, it will have been kept inside your "~/Library/iTunes/iPhone Software Updates" folder. That's where it is on a Mac, I don't know where it is on a PC.
If you didn't already make a backup of this file before you upgraded to iOS 6, Apple told the computer to automatically delete it and replace it with the one for iOS 6. I can't tell you where to find a replacement, sorry.
Also, be aware that anywhere inside ~/Library is not somewhere Apple wants you tinkering around in. That's why as of OS X 10.7 and later, they don't make it directly accessible. Anything that goes on in there is really designed to be done by the OS and by the programs you run,
not directly by you. Changing things in there willy-nilly can make all kinds of things not work right. You have been warned.
That said, backing up a file you're legally entitled to (by the fact that you own an iOS device that will run it) is fully within your rights, and copying it (as opposed to changing it in any way) shouldn't present any functionality problems. So to get to the correct folder, just go to the "Go" menu in the Finder, select "Go to Folder," and type in the correct path to that folder. As long as you typed it in correctly, a Finder window for that folder should open. Again, I heartily recommend against deleting, moving, or changing any files in there. Just copy what you need.
As above, if the computer has already replaced and deleted this file, then you've missed your chance. There may be other ways out there to find one, but it's not one you're legally entitled to (you're legally entitled to
your copy). Maybe you can see if it's available via your Time Machine backup. Beyond that, I can't help you. Sorry.
Moving on, if you want your iOS device to look and work how it did before you ever upgraded to iOS 6 (with your sounds, wallpapers, apps, music and photos, etc. in the same places), then you will also need a backup of your own data on the phone, done as close as possible to
just before you upgraded to iOS 6. If you generally back up to the computer, you would have just hit the "Sync" button in the iTunes window. If you generally back up to the iCloud, I still recommend before any major iOS device upgrade, to back up to your computer by option-clicking the iOS device's icon in the left column of iTunes' window, and selecting "Back Up" from the contextual menu that pops up. This is because if you rely on Apple's iCloud backup of your iOS device alone, it
will have changed things when you upgraded to iOS 6, and Apple hasn't set iCloud up to allow easy downgrades, because they want to keep the ball rolling
forward.
If in doubt at all, back it up yourself. And also realize that any content you've put on the iOS device or changed since upgrading to iOS 6 (particularly irreplaceable, personally-made things like videos you've shot)
won't be in that most recent iOS 5.1.1 backup of your data (because you shot it after you upgraded to iOS 6). So back such things up some other way (say, to iPhoto), before downgrading back to iOS 5.1.1.
What you do:
If you did happen to make a backup of your iOS 5.1.1 install file, then you can put your iOS device into DFU mode (if you don't know how, you can search for how to do it) and then restore the 5.1.1 install file onto the device. The way to select the 5.1.1 install file as opposed to the 6.0 install file is to hold down the "Option" key as you press the "Restore" button in iTunes. This will allow you to navigate to the 5.1.1 install file, wherever you've put it, and select that (as opposed to the most recent one in the folder discussed above, that Apple uses by default) as the source from which to restore.
Once this iOS 5.1.1 software is restored to your device, you're half done. Then, you'll want to use the most recent backup of your data from before you upgraded (discussed above), to put back onto your iOS device. Once that data is put back on, it should then be back to how it was before you upgraded to iOS 6. Be aware, how long it will take is related directly to how much data you had on your iOS device: the more data, the longer. Once that's done, you can then make your own decisions about what and how to put back content you added/changed under iOS 6.
Finally, one more point to be aware of: if iOS 6 upgraded the firmware on your device in some way that iOS 6 needed to work, but which iOS 5.1.1 is not compatible with and it can't be overwritten by the iOS 5.1.1 install file, then downgrading won't work. I don't know which devices, and in fact whether any of them, this will happen to. It didn't to mine: my downgrade just worked, and it put all of the versions of firmware that are available to view under in the Settings app under General>About back to what they had been before under iOS 5.1.1.
As far as I know if the firmware is changed by iOS 6 in a way that is not downgrade-able, then iTunes should just not allow you to perform the downgrade, and return your phone to working (such as it does) with iOS 6. Keep in mind that I am not in any way affiliated with Apple, ie. not an Apple software engineer, so I don't know that for sure. Your mileage may vary, and the fact that it worked on my iOS device doesn't mean it will work on yours. You're responsible for your own decisions and actions.
So I've said my piece. I don't think it should necessarily be simply and flatly said that "you can't" downgrade from iOS 6.0 to iOS 5.1.1. Maybe you can't on some devices, in some configurations. But I did, and I did so completely legally, without invalidating any of the services Apple provides through iOS 5.1.1, and without any highly technical or questionable shenanigans. I just know how to do some things, and researched how to do the parts I didn't. And I was open to
trying it. There may be iOS devices and situations for which the method I used won't work, and I can't help you with those. But the Internet may be of help to you.
Good luck!