cordless phone vs telephony

cordless phone

noun
  • A telephone unit that has a battery-powered telephone receiver/handset that uses RF signals and antennas to communicate to the wired base station instead of a cord, which is attached to a landline and functions as a charger for the receiver. 

telephony

noun
  • The study and application of telephone technology. 

  • The act of sound transmission via the electromagnetic spectrum. 

How often have the words cordless phone and telephony occurred in a corpus of books? (source: Google Ngram Viewer )