If you're buying a new iPhone, and the old one will be disposed of in some fashion, it will be a good idea to create a complete backup of that old iPhone just before it's decommissioned. Here's how to do it.
With iTunes 11 running on your Mac or PC, connect your iPhone with the USB cable. On the upper right side of iTunes, you'll see a "device" button. Click it and then click the iPhone icon.
In the tab buttons at the top of iTunes, make sure you've select the Summary tab.
Then you should see a page like this:
In the "Backups" section, select:
- Automatically back up to "iCloud" or "This computer." I recommend, for starters, you back up to your Mac. It will be faster and more private. You can even encrypt the backup with a password if desired.
- In the block on the right (shown in red), Click "Back Up Now." The application data and settings on your iPhone will be saved in a complete backup (except the OS itself): your settings, plus the selected sync options for music, movies, books, etc.
Because your apps, music, books, movies, etc. are already stored in iTunes (and presumably backed up by you with Time Machine, at least), the backup archive doesn't actually contain all that content: just references (lists) to what was synced to the iPhone.
Of course, if you don't have a Mac or PC, Apple has made the iCloud option available. On your iPhone: Settings -> iCloud -> Storage & Backup -> iCloud Backup = ON.)
When you get your new iPhone, reverse the process. Connect it to your Mac and select "Restore backup". (Or, during the activation and set up process, you could elect to restore from iCloud.) Because the OS is not overwritten in either case, iOS 7 on your new iPhone will remain intact.
If you have elected to encrypt your backup then all your email passwords will be preserved. If you have elected not to encrypt the backup, those plaintext passwords were not included in the archive for the sake of security. You'll have to re-enter them on your new iPhone.
Note that if you merely elect to do an iTunes Sync (Settings -> General -> iTunes Wi-Fi Sync) only the items you've selected to sync with the iPhone in iTunes elections will be copied. Settings are not synced.
ITunes Wi-Fi sync doesn't preserve settings.
Finally, the name of your iPhone in the iTunes summary page is an editable field. If you click it you can rename the new iPhone, and that label will be used for all future backup file names.
The name of your iPhone in ITunes is editable.
Another housekeeping task to attend to at this time is to force a transfer of purchases from your old iPhone back to iTunes. We have noticed that, during a routine sync, sometimes, not all updates that one applies on the iPhone get transferred back to iTunes. You can force this under the iTunes File Menu -> Devices.
Use this to force app puchases and updates back to iTunes.
Finally, note that Apple typically posts a new version of iTunes just before a major new IOS release, so watch for that before you proceed.