INT B3 - ZIPKEY v2.0+ - DETERMINE STATE FOR AREA CODE
        AH = 80h
        BX = telephone area code (decimal)
Return: CF clear if successful
            AL = ZIPKEY state code
            DX = first ZIP region for state (03E8h if Canada)
            CX = number of ZIP regions in state
        CF set on error
            AL = FFh
            DX = 03E9h