Well this depends. In theory this is possible, but not practical in many cases. In order to get voicemail services to work, the user requires a phone system license. You would need to enable the user with a number in Microsoft Teams that doesn’t need to be a real number if you don’t need it.
You’d then have to configure a route between your existing system and the Direct Routing SBC for the number range you’ve chosen.
Once that has been done, you’d need to tell your users to configure their forward no answer settings to their Teams number. If they are not using Teams, this will forward directly to their voicemail service. If they were using Teams, they would get the call offered in Teams first before forwarding to voicemail.
One note here is that their voicemail will be delivered to Exchange Online, so this is a pre-requisite as well (or configure hybrid for on-prem SMTP delivery)