The following lines were added (+) and removed (-):
Touch-tone land-line phones began to replace rotary dial. Bell Telephone introduced Touch Tone dialing in 1963 using the DTMF standard. '''DTMF''', or Dual Tone Multi-Frequency, is used when pressing a numbered key on the telephone dial pad. A specific DTMF tone is generated for each numbered key. The land-line phone system can then "listen" and decode that tone to determine which key was pressed, enabling dialing. Each DTMF "tone" is actually two tones - a low-frequency tone and a high-frequency tone - combined. (Hence the name "dual tone multi-frequency".) Touch-tone land-line phones began to replace rotary dial. Bell Telephone introduced Touch Tone dialing in 1963 using the DTMF standard. '''DTMF''', or Dual Tone Multi-Frequency, is used when pressing a numbered key on the telephone dial pad. A specific DTMF tone is generated for each numbered key. The land-line phone system can then "listen" and decode that tone to determine which key was pressed, enabling dialing. Each DTMF "tone" is actually two tones - a low-frequency tone and a high-frequency tone - combined. (Hence the name "dual tone multi-frequency".) The term Touchtone was used to market the DTMF advancement. Touchtone / Touch-tone was actually a trademark of Bell Telephone. The numbered key layout was actually the result of years of research prior to its introduction. Early residents had to share a phone line with multiple families or homes in a neighborhood. The '''Party Line''' implemented selective ringing to distinguish one subscriber from another on the same line. This was later replaced with a more advanced selective ringing system so that only the individual phone in the family home the call is directed to rings. If there were four families on a single party line, and a call was directed to family #2, only that phone would ring. However, any of the families on the party line could pick up the receiver and eavesdrop on the other family's phone conversation.