The regular analog telephone
service, using copper wiring, as opposed to ISDN, ADSL, and other digital phone
Internet Telephony; Voice over IP.
"Plain Old Telephone System." YourDictionary, n.d. Web. 16 May 2018. <http://www.yourdictionary.com/plain-old-telephone-system>.
Plain Old Telephone System. (n.d.). Retrieved May 16th, 2018, from http://www.yourdictionary.com/plain-old-telephone-system