Any number of rural areas have post office box only delivery. If you search using usps.gov, it can tell you whether or not the area falls into that category (try 26209, for Snowshoe, West Virginia, for example, although it's a peculiar example).
My mother lives in an unincorporated area in West Virginia which now has rural route delivery (but previously was post office box only). She is "served" by three different zip codes, one (where she actually lives) with no delivery to her, another that is the closest post office (for her post office box), and a third that is the "delivery" post office (for her star route/rural route/"highway" contract box which she pretty much refuses to use). It makes FedEx, UPS, and (formerly) DHL delivery a nightmare, too, because the addressing has changed every few years.
You still following me?
Needless to say, she received her smart cards via her post office box.
justen