KA7OZO is an amateur radio callsign assigned to me by the F.C.C. There is only one KA7OZO.  If you have been around for a while you will know that a KA7 call is a lot older than the more recent KJ7 calls, in fact I think they are about ready for the KK7 calls. A callsign is nothing more than an identifier. Each country has different prefixes and a list can be found at http://www.arrl.org/international-call-sign-series.