computer network vs voicemail

computer network

noun
  • A group of computers that use a set of common communication protocols over digital interconnections for the purpose of sharing resources located on or provided by the network nodes. 

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 computer network and voicemail occurred in a corpus of books? (source: Google Ngram Viewer )