In 1983 , the U.S. Postal Service began using an expanded ZIP code system that it called ZIP +4 , often called `` plus-four codes '' , `` add-on codes '' , or `` add ons '' .
In 1983 , the U.S. Postal Service began using an expanded ZIP code system called `` ZIP + 4 '' , often called `` plus-four codes '' or `` add-on codes . ''