snail mail vs voicemail

snail mail

noun
  • Mail sent physically in the post, especially as compared to email. 

voicemail

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

  • An individual message on such a system. 

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