A few years ago the New York Times published a story about Voicemail usage being on the decline. If the wrote that same story today, my guess is that they would find that on the decline was an understatement. It's more than likely in free fall.
Basically, most of the people I know text before they call someone, or schedule calls for business. In my own case, I'll use a conference bridge vs. just calling someone at an agreed upon time in order to avoid the hassle of a call coming in just before the scheduled call is to occur on either side. A conference call is like an appointment, evidenced by the number of people who often say, "I'll have to cut this short, I have a call scheduled in a few minutes" or "I have a hard stop at...." Both are tells that your time is limited with them, and like the other people, you should have scheduled your call.
But voicemail as we know it is from the mobile operators is rather antiquated. You can't forward the message easily. The message can't be downloaded, usually. And the message is not usually transcribed. Those three functions have been around for a long time from third party service providers, but while those services have seen users stick with them, those same people are the ones who are not using voicemail from the mobile operator.
But the biggest deathblow voicemail has is it's own premise. Too many people don't like playing voicemail tag. That's the endless game of leaving a message to get a message back some hours later, only to have it lead to yet another message being left.
It's time to be able to turn off voice mail....I just wonder which mobile operator will offer that option first, and reduce your bill too....now wouldn't that be an uncarrier move.....?