Push-button phones replaced rotary dials with button (keypad) input. NTT introduced them in Japan in 1969, and "Push-Phone" is NTT's registered trademark. Pressing a button generates DTMF (Dual-Tone Multi-Frequency) signals - two simultaneous tones that the telephone exchange detects to identify the dialed number.
Push-button phones transformed telephone usage. Rotary dials took about 1 second to dial "0," while buttons enabled instant input. More importantly, DTMF signals transmit during active calls, enabling IVR menu navigation, telephone banking PIN entry, and ticket reservation seat selection - interactive services impossible with rotary phones.
Smartphones inherit push-button technology. The keypad displayed during calls sends DTMF signals for navigating call center IVR menus ("Press 1 for..."). Though smartphone calls are digital (VoLTE), DTMF signals are maintained for compatibility.
A small number of rotary phones remain in use as of 2024, but they cannot interact with IVR or automated services, making push-button migration practically necessary. See telephone evolution history for the rotary-to-push-button transition.