telephone vs voice mail

telephone and voice mail both are nouns.

Word	Noun	Adjective	Verb	Adverb
telephone	Yes	No	Yes	No
voice mail	Yes	No	No	No

As nouns, voice mail is a hyponym of telephone; that is, voice mail is a word with a more specific, narrower meaning than telephone:

telephone: transmitting speech at a distance
voice mail: a computerized system for answering and routing telephone calls; telephone messages can be recorded and stored and relayed

Other hyponyms of telephone include voicemail, call, phone call, telephone call, call forwarding, call waiting.

telephone (noun)	voice mail (noun)
electronic equipment that converts sound into electrical signals that can be transmitted over distances and then converts received signals back into sounds	a computerized system for answering and routing telephone calls; telephone messages can be recorded and stored and relayed
transmitting speech at a distance

telephone (verb)	voice mail (verb)
get or try to get into communication (with someone) by telephone