the objects help to turn most landline telephones into MIDI controllers with 12-16 buttons. An MT8870 IC is needed to decode the dial signal to a four bit signal entering 4 gpio pins and an additional trigger while the dial button is pressed.
the telephone needs to work on DTMF (Dual Tone - Multi Frequency) signaling which most telephones nowadays do. One can clearly hear the familiar dial tone, which is actually two frequencies playing according to this matrix:
The circuit for the DTMF decoder chip MT 8870. The ports 11-15 need to be connected to gpio pins.
the objects work independently. the "code" object has an extra output which triggers when a certain combination of buttons was pressed.
This is the subpatch hug/dtmf/dtmf_core.axs which serves as an example: