Can you block an entire area code on an iPhone?

I have a 405 area code (Oklahoma), but am constantly getting calls from 402 (Nebraska)-- I assume this is an error when people are typing in the number, as 2 is directly above 5 on a 3x3 number layout. Nonetheless I get 1-2 calls EVERY DAY from Nebraskans who can't double check their numbers before they call.

(Like, for two months this guy hounded me saying I owed him $500 despite me saying that he had the wrong number and to try with a 402 area code.)

I have an iPhone 4 with iOS 6.

Your telephone service carrier, or the people at Apple might be able to help you with this. Your irritation at receiving constant calls from idiots who don't double check their work is fully understandable. It might be challenging, though, to block out an entire area code. Try contacting the company which provides you with phone service or checking one of the Apple forums online.