caller-up vs telephoner

caller-up and telephoner both are nouns.

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

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

Other synonyms of caller-up include caller, phoner.

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