telephone company vs telephone service

telephone company and telephone service both are nouns.

Word	Noun	Adjective	Verb	Adverb
telephone company	Yes	No	No	No
telephone service	Yes	No	No	No

As nouns, telephone company and telephone service are synonyms defined as:

telephone company and telephone service: a public utility that provides telephone service

Other synonyms of telephone company include phone company, phone service, telco.

telephone company (noun)	telephone service (noun)
a public utility that provides telephone service	a public utility that provides telephone service