call up vs ring back

call up

verb
  • To call on the telephone. 

  • To select e.g. to a sports squad. 

  • To summon (someone) to report for military service. 

  • To retrieve from personal or computer memory. 

noun
  • An order to report for military service. 

ring back

verb
  • To return a phone call. 

  • To make another phone call to the same person. 

How often have the words call up and ring back occurred in a corpus of books? (source: Google Ngram Viewer )