Each number from 0 to 9 is uniquely identified with a DTMF code that can be received and interpreted on the receiver side. DTMF code signaling enables reception of information from the end user e.g. PIN codes during a voice call.
How are DTMF codes used in the telecom industry?
Today’s mobile telephones use a digital process for standard calling and messaging, so DTMF codes are not used when connecting to the mobile network base station. However, they do support DTMF codes for a number of important use cases: