iOS remembers custom ringtones through device swaps

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If you get a new iPhone and restore it from an iCloud backup, your custom ringtones will not be restored, and all your alarms and ringtones will be set to the default Marimba. However, if you sync your new phone with the same iTunes library as your old phone, and the ringtones are restored, all your alarms and phone rings that had custom ringtones assigned will revert to the custom tones automatically.

Thanks Zev Eisenberg

iTunes 11 shows more details about what’s stored on your iPhone, iPad

If you plug your iPhone or iPad into iTunes and mouse over the colored storage bar at the bottom of the device details page, you’ll see more information about what and how much stuff is on your device.