At first I not understand how to use but is just enable and select the notification that you want and the app will delete for you, if I am not mistaken I am using this app about a month and since then haven't get in my phone one voicemail, he did what he was meant to do, but, I THINK, that by he work on the background as a second plan app he is eating more battery than normal...
Remove Voicemail at Google Play market analyse