telephony vs telecom

telephony and telecom both are nouns.

Word	Noun	Adjective	Verb	Adverb
telephony	Yes	No	No	No
telecom	Yes	No	No	No

As nouns, telecom is a hypernym of telephony; that is, telecom is a word with a broader meaning than telephony:

telephony: transmitting speech at a distance
telecom: (often plural) systems used in transmitting messages over a distance electronically

Other hypernyms of telephony include telecommunication.

telephony (noun)	telecom (noun)
transmitting speech at a distance	(often plural) systems used in transmitting messages over a distance electronically