Dual Tone Multi Frequency (DTMF) - Signal Identification Wiki
What is DTMF (dual tone multi-frequency) and how does it work?
Taidacent DTMF Decoder/Encoder Full Form Dial Tone Generator Dual Tone Multi-Frequency Audio Decoding Digital Display: Amazon.com: Industrial & Scientific
DTMF Dialer for an Old Pulse Phone | BinaryMagi Inc.
Simply DTMF Tone Generator - Apps on Google Play
DIY - DTMF Tone Generator and Decoder Circuits
CircuitWerkes GEN-r8 Programmable DTMF Tone Encoder/Generator - ProAudio.com
Generate DTMF Tones Only Using Arduino - Arduino Project Hub