telephoner vs caller-up

telephoner and caller-up both are nouns.

Word	Noun	Adjective	Verb	Adverb
telephoner	Yes	No	No	No
caller-up	Yes	No	No	No

As nouns, telephoner and caller-up are synonyms defined as:

Other synonyms of telephoner include caller, phoner.

telephoner (noun)	caller-up (noun)
the person initiating a telephone call	the person initiating a telephone call