Back in the days of the original iPhone, Apple printed each device's serial number right on the back of the iPhone. This is no longer the case, but every once in a while iPhone owners still need their serial number. Checking for warranty coverage or scheduling a repair typically requires entering this information, as each iPhone has its own unique number.
Keeping the carrier settings file on your iPhone up to date ensures the best wireless performance on your carrier's cellular network. Typically, the carrier will push updates to subscribers' devices automatically. Then iOS will ask if you'd like to install these new carrier settings with a prompt.
Shake to undo makes it easy to quickly undo typing on the iPhone, iPad and iPod touch. After shaking an iOS device, a confirmation dialog appears. For situations where the undo dialog gets in the way of other activities on the iPhone, the feature can be switched off. Shake to undo is enabled by default.
The iPhone, iPad and iPod touch remember Bluetooth devices forever after the first pairing. For iOS users with a long list of Bluetooth devices, it might be time for some house cleaning. Removing old or unused Bluetooth devices from Settings can reduce confusion and simplify your life. Once paired, a Bluetooth device can easily be removed.
AirPods and headphones connected to the iPhone, iPad or iPod touch normally deliver audio in full stereo. In fact, even the external speakers on recent models offer stereo sound. However, there are times when mono audio may be preferred. One reason why iPhone owners might disable stereo would be to share AirPods or a single set of headphones between two people.