Sounds like you've never used MetroPCS in northern California.
Imagine that, after buying the car, you turned the key to start the car and instead a lawyer popped out of the glove box holding out a contract insisting that you were not allowed to start the engine unless you signed it. That's not fair. You have to be permitted to decline that contract, and if the engine manufacturer refuses to let you use that engine as a result, they should buy it back from you.
No. No, I don't. I don't even slightly get it.
For starters, why are you referring to a date in 1997 as if it hasn't yet occurred?
Next, why did you end your second sentence with the word "too"? Were you addressing an individual other than who you addressed in your first sentence?
Does this include network traffic entering the country? Yikes.
Holy frijoles. You just conspired to commit a crime. See how easy that was?
1) Ask new visitors to enter their ZIP code.
2) Check the ZIP code against a simple array of "acceptable" local ZIP codes.
3) Store it as a cookie in their browser (so they don't get asked over and over)
Remote users (from Kentucky or Afghanistan) have no idea which of the thousands of available ZIP codes you'll accept visitors from, but local users who give you a simple and honest answer will be allowed in quickly.
Brute-forcing your valid ZIP codes is certainly possible, but not worth the trouble.