What Refugee is referring to is picking up the caller's ID and ringing that number. It is fairly easy for a 'phone to store that ID (the caller's number) and return the call by ringing that number. The bit which requires specialist circuitry is to extract that ID as it is stored somewhere in the network when the caller has suppressed communication of the ID to the called party's 'phone. I hope this clarifies the matter.
Incidentally, there is quite an interesting
Wikipedia article about DTMF, mentioning the four extra tones (A, B, C, D), though giving no indication of how they may be used.