OK, disclaimer: You might lose a couple of things. However, in my experience, I've lost nothing. Do this at your own risk. I find it the safest restore procedure to setup new or replacement devices.
Background: I moved recently, and my iPhone was setup to sync with my old computer. So, since I'm now primarily using a MacBook Pro (Retina!) every day, I was met with a problem: How can I get all of my stuff over to a new iPhone? The iPhone 5 is coming out soon, and if you've ever had your phone replaced… this is a legitimate problem.
Before you replace your device, do three things...
- Make an encrypted iTunes backup of your iPhone on your computer via USB. Click on your iPhone in left-column of iTunes or find it in the navigation menu. Make sure the “Encrypt iPhone backup” checkbox is checked (turned on), and then click the “Back Up Now” button. You can do this without syncing. Without the backup being encrypted, some settings are not backed up.
- Download any Apps/Music/Books to iTunes on the computer that you'll be using from now on, if you want them on your device. You may be able to transfer some of these using the “Transfer purchases” in the “Devices” menu, that's inside the “File” menu.
- Finally, make an iCloud backup on your device (using Settings). This is optional, but recommended as a good fallback.
Once you've done all of this … you'll have a backup in iCloud (just in case), a complete backup in iTunes of all of your data/settings, and a copy of all of the content you want on your new device… such as the Apps themselves and any of your music that wasn't on your computer in the first place.
Now that you're ready, here's where things get tricky. You'll need to do multiple “restores” of your device to get everything correct.
Restoring to the new device, the first time
When you have your new device … do not restore the device from iCloud when setting it up, and instead restore it from iTunes. You can do this the first time you plug into iTunes, by restoring from a previous backup. You should be prompted to do this.
If you've synced your device with this particular computer originally, the encrypted backup you made should restore all content nearly exactly and begin syncing your Apps automatically. If it was with a different computer originally, you'll be minus any content and Apps, but with settings such as your wallpaper, passwords, and Wi-Fi networks.
So, to get everything back the way it was, select all of the Apps, Music, Books, Podcasts, etc. that you want within iTunes and sync them to your device. It may prompt you in saying that it was “synced with another iTunes Library” and that all of your content will be erased. This is OK (you have two backups), and it will simply put all of your Apps onto your phone across multiple home screens.
At this point, DO NOT OPEN ANY OF THE APPS ON YOUR DEVICE YET! The reason for this… is that iTunes, when restoring data from backup, will not overwrite newer files. By opening Apps on your device before you've restored their data (again below), you will create new data files within them that will be “more up to date” than your backup. This will prevent their restoration.
If you make the mistake of opening an App… it will not replace your data with the backed up version you're trying to recover. So, don't do that!!
The final step: a second restore to the new device
Right-click your device on the left-hand column of iTunes (again), and click “Restore from backup…”. Yes, we're restoring it again. From the screen that appears, select the backup of your old device that you originally restored from (again), and restore your device again.
What this does is it restores your device and App settings again without removing any of your newly added content, including Apps, Music, Books, etc. — When this is complete, your Apps will still be there (the ones you just synced), but all of your data, App folders + organization, and other settings will be restored, too! Go through the “Settings” App on your phone and test each App out after this to be sure everything is the way you want it. (It should be OK to open your Apps now, as their data should be present from this second restore.)
Now, if you made the mistake of opening an App before this restore had taken place, you will have to reconfigure that particular App from scratch. However, the others (or all of them if you didn't open any) should be fine based on your backup!
Switched devices after switching computers? Just follow these steps and you should be good to go. Furthermore, your device should be configured to sync with your new computer from now on. Hooray!
Keep in mind, that any Music, Apps, or Books you don't have on this computer that you're connected to cannot be restored as they don't exist anywhere except your old device. This content is not backed up. That's why in Step #1 you need to have this sorted out first within iTunes. There is third-party software available to copy songs and other multimedia from iOS devices. Good luck!