I do know mine..but that is only because it is the same as our house number. Although it took a couple of years of living there before we saw a piece of mail that had the +4 code on it. Does the USPS have a look up on their website for it? I don't know of an easy way to find out with out having to go down to the Post Office. So that might be a big part of it even though its been around for ever.