third class vs voicemail

third class

noun
  • A reduced-rate mail service for printed matter. 

  • The cheapest accommodation on a train or ship. 

voicemail

noun
  • An individual message on such a system. 

  • A computerized interactive system for storing, processing and reproducing verbal messages left through a conventional telephone network. 

How often have the words third class and voicemail occurred in a corpus of books? (source: Google Ngram Viewer )