Do you want to update the contacts that were using this line to use your other line?

rafaela21 Said:

"Do you want to update the contacts that were using this line to use your other line?"

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Multiple Lines on an iPhone:

It appears you have more than one line on this phone. So, it is asking you which to update your Contacts list with.

Go to: Settings > Cellular. Does this screen look somewhat like this?:

rafaela21 Said:

"Do you want to update the contacts that were using this line to use your other line?"

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See this site: "Used as Secondary" in XR settings menu - MacRumors