Hi Abaci, after FS-8875 was merged yesterday in PR 775 I have tested avmd on your Verizon voicemail (contains 1000hz beep) and on another Voipfone voicemail (contains beep of lower frequency, 724.1914 is detected). Detection of tone works just fine while not giving many false positives in the same time. But you should note the avmd module is in beta stage so not everything is working as expected yet. In case of Verizon sometimes it gives false alarm on silence, this can be handled at this moment by adjusting avmd session parameters AVMD_SAMLPE_TO_SKIP_N increase BEEP_TIME increase SAMPLES_CONSECUTIVE_STREAK increase VARIANCE_THRESHOLD may need to decrease or starting avmd after 3 - 4 first ring tones. Regardless of this it will be treated in more generic way - by adding of estimation of amplitude. Related to this is a need for adjusting parameters on a basis of expected characteristics of incoming signal, e.g. SNR. And it should be possible to be set the settings on a per call basis. So you may wish to checkout master branch, build, test, and let us know the results. cheers, Piotr