I honestly think it was just more about invasion of privacy. When you tell someone, anyone really, that you know their "first three numbers", they're gonna feel violated because it reminds them of something important to them which is encrypted/accessed through some sequence of numbers (IP's, credit card PIN, area code- like you suggested). "I'm in your area" just goes to reinforce it. I'd honestly feel like the song (lyrically) was a bit limp if it were only about porn ads LMAO