telco vs public utility company

telco and public utility company both are nouns.

Word	Noun	Adjective	Verb	Adverb
telco	Yes	No	No	No
public utility company	Yes	No	No	No

As nouns, public utility company is a hypernym of telco; that is, public utility company is a word with a broader meaning than telco:

telco: a public utility that provides telephone service
public utility company: a company that performs a public service; subject to government regulation

Other hypernyms of telco include public-service corporation, public utility, utility.

telco (noun)	public utility company (noun)
a public utility that provides telephone service	a company that performs a public service; subject to government regulation