All the new Telephones now uses Dual-tone multi-frequency for Dialing. Gone are the days of Pulse Dialing. Pulse Dialing used Rotary dialing. A switch was made to open and close to make numbers of pulses depending upon the number dialled. It was producing a almost and square wave forms.
With advances in the PABX and Digital technolgy Touch tone Dailing has become the order of the day. Click on the link below to know about dual-tone frequencies.
http://en.wikipedia.org/wiki/Dual-tone_multi-frequency
