This app is grey with a gear icon on it.
 It's near the top of the page.

If your phone uses U.K. English, this option will be called "Mobile Data"., If your phone displays this option, it's unlocked; otherwise, your phone is locked.On some phones, such as AT&T ones, you'll first have to tap Cellular Data Options before you can view the "Cellular Data Network" option.
In exceptionally rare cases where your carrier has given you a SIM card that lets you change your iPhone's Access Point Name (APN), having this setting won't necessarily mean that your phone is unlocked. If your phone has a SIM card like this, proceed to the next method.
Open your iPhone's Settings.
Tap Cellular.
Look for an option entitled "Cellular Data Network."
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