I used to think that was a dumb move on the part of the scammers, and probably would only be effective in a small town where most of the people you know have the same prefix… Then I realized that most of the successfully scammed victims probably live in those small towns.

Great point! I hadn't thought about that. It's my cell that gets hits like this, so the prefix is extra-irrelevant.

I once had a series of spam calls that reported their number as being my own phone number.

Made it really easy to spot them, and was very funny.

This probably had some logic historically with landlines—a neighbor is calling. It’s an anti-pattern for cell phones in the “wrong” area code. Used to get this a lot. Rarely today.