Probably, but I have calls whitelisted and no voicemail. They can call all they like, it just rings and then they hang up.
They are getting around that by spoofing. I got one earlier from some marketing people coming from a Verizon number and it was poonjab.
There are 3 numbers whitelisted in my call book. My parents, a good friend, and a trusted co-worker that can call if something is wrong.
I supposed they could spoof one of those, but it would be quite the lucky chance on their part.