Hmm, have you ever answered these calls to see if they're coming from an automated system? I pretty sure this has happened to me before but I was getting a 1 second voicemail. They only thing I can think of is it's a automated calling system disconnecting shortly after the voicemail starts to record.
Just checking in to see if you've answered these calls or know if these are coming from automated systems?
I now get these just about daily. I've answered one or two by mistake, and can confirm they are indeed robocalls. The routine is reliable: an unknown number from my area code rings, I decline it, 15 seconds later a voicemail of one second with no audio whatsoever appears on my iphone.
Regardless of origin, it doesn’t make sense for the system to forward a voicemail notification for a one second long message that contains no audio content. Either a minimum time (can anyone relay anything meaningful in under, say...3 seconds?) or audio peak level should by themselves disqualify these as voicemails. I emphatically urge T-mobile (and/or apple, I suppose, since this may be specific to Visual Voicemail) to remedy this; I can't be alone in nearing the end of my patience for it