If you are looking for some kind of voice recognition like
DTMF detection, then it is not possible to do with Nokia 30.
Nokia 30 can for example generate DTMF tones, but it can not
You can use digital audio lines of the system connector of the Nokia30.
There are four different digital audio signals on the system connector of the terminal: PCMDCLK, PCMSCLK, PCMTX and PCMRX. PCM (Pulse Code Modulation) is a method for the transmission of digital audio data. The format of the data transmission is sign-extended 13 bit linear code.
Please, go to the:
and choose "Application Development" and
download the "Audio Application Note For Nokia GSM Connectivity Terminal" document to find out more information
about the audio lines of the Nokia 30 terminal.