Simple VAD (Voice activity Detector) implementation
Based on the highest frequency you expect in your signal define the sampling rate. Accumulate samples for 10 seconds and carry on an FFT, in groups to allow for enough energy in bins based on expected frequencies.


silence will have a typical low power with noise structure.
Dial tones and ringtones will have distinctive, pre specified bins.
Voice will have higher power than noise with some similarities to noise. You might fine tune your analysis but I do not think you will need it.