System to track what Zip Codes my vendors service
I would say you would have:

Table: vendor
  id, name, etc

Table: vendor_area 
  id, vendor_id, area_code_id

Table: area_code
  id, area_code, country_id, region_id (etc)

I'm suggesting that not knowing your business. But I would hate you go in a naive route assuming that you'll do US only and in a couple year you have to redesign the whole thing. The above will give you flexibility to expand and add more meta data to your areas/regions being covered.