Knowing what numbers are real through an official publication is very good, but it only allows you to place trust in calls you make, not calls you receive, because making calls doesn't involve caller ID, receiving calls does, and caller ID is spoofable.
That's the number one rule though. If someone calls you claiming to be your bank, just say "I'll call you back"
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That would take nothing to implement. Services like Truecaller already do live caller ID against databases on iOS / Android. All it would take is a sensible register of verified numbers
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