Which hardware does a computer needs to understand the DTMF signals produced by the phone..
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Telecommunication cards
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Telephony board or telephony card
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Keypad
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Speaker phones and keypad
A telephony board or card is necessary to interface between the telephone network and the computer, converting DTMF tones into digital signals. These specialized cards contain hardware to decode touch-tone signals. Standard telecommunications cards or simple keypads lack this capability.
DTMF (dual-tone multi-frequency) tones are generated at the phone/keypad end when a caller presses a key. For a COMPUTER to understand/decode those incoming tones (e.g. in an IVR, voicemail, or call-center system), it needs dedicated hardware capable of detecting and decoding the two simultaneous audio frequencies that make up each DTMF tone — this is a telephony board or telephony card (e.g. Dialogic-style cards), which contain DSP/decoder circuitry (historically chips like the Holtek HT9170) purpose-built for DTMF detection. A keypad is the tone-generating hardware on the caller's phone, not the decoding hardware on the computer's side, so it answers a different question (how tones are produced, not how a computer understands them).