WordNet records no synonym and no antonym for area code. It is the only member of its synset, which is common for technical, taxonomic and single-sense vocabulary — there is no other English word that means the same thing. The broader and narrower terms below are the useful relations in that case.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
a number usually of 3 digits assigned to a telephone area as in the United States and Canada
Synonyms, antonyms and the broader and narrower relations for area code come from Princeton University’s WordNet. Full sources and licences.