subscriber line vs telephone line

subscriber line and telephone line both are nouns.

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

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

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

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