caller vs telephoner

caller and telephoner both are nouns.

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

As nouns, caller and telephoner are synonyms defined as:

Other synonyms of caller include caller-up, phoner.

caller (noun)	telephoner (noun)
a social or business visitor	the person initiating a telephone call
the person initiating a telephone call
the person who convenes a meeting
someone who proclaims or summons in a loud voice
a person who announces the changes of steps during a dance
the bettor in a card game who matches the bet and calls for a show of hands
an investor who buys a call option

caller (adjective)	telephoner (adjective)
providing coolness
fresh