The concept of people leaving audio messages _with a reasonable expectation that someone will listen to them_ is (thankfully) dying out, at least among my social circles.
You can leave a message if you want, I'm not going to listen to it. The only entities that make unexpected phone calls are scammers and bots.
Given that I never get ham voice calls, it is reasonable for me to assume that any voice mails that I receive are therefore spam (but, no, you're right, I don't recall ever noticing a spam voice mail. But then I wouldn't notice one, whether it existed or not, because I don't check them)
You must not be in the United States then. Pretty much guaranteed every phone number in the US has received at least one “automobile extended warranty” voicemail.
