call box vs Post-Office box

call box and Post-Office box both are nouns.

Word	Noun	Adjective	Verb	Adverb
call box	Yes	No	No	No
Post-Office box	Yes	No	No	No

As nouns, call box and Post-Office box are synonyms defined as:

call box and Post-Office box: a numbered compartment in a post office where mail is put to be called for

Other synonyms of call box include letter box, PO Box, POB.

call box (noun)	Post-Office box (noun)
booth for using a telephone	a numbered compartment in a post office where mail is put to be called for
a numbered compartment in a post office where mail is put to be called for