[DugwayDuke]

Next to useless. Spammers, salesmen, etc., have learned to spoof legitimate numbers. They can make your phone think it’s any number they want it to be.

[FreedomPoster]

Often one in your area code / exchange, to make it seem like it might be someone you know.

[Vigilanteman]

I can't figure out the thought process behind that. Do they really think they can sell you something after their deceit is discovered?

I've asked them that very question and am surprised how many are genuinely embarrassed.