Why does some of my incoming calls on my iPhone have the plus before the area code and some don't?

The presence of the plus sign (+) before the area code indicates that the number is formatted as an international call, while numbers without the plus are typically formatted for domestic dialing. Incoming calls may vary in format based on the caller's phone settings or the international dialing protocols used. If a contact is saved with the international format, it will show the plus sign, whereas local numbers saved without it will appear without the plus. This discrepancy is common and generally does not affect call functionality.