telephone line vs subscriber line

telephone line and subscriber line both are nouns.

Word	Noun	Adjective	Verb	Adverb
telephone line	Yes	No	No	No
subscriber line	Yes	No	No	No

As nouns, telephone line and subscriber line are synonyms defined as:

Other synonyms of telephone line include line, phone line, telephone circuit.

telephone line (noun)	subscriber line (noun)
a telephone connection	a telephone connection
the wire that carries telegraph and telephone signals