Voicemail alone doesn't have information about someone's schedule.

"I'd like to schedule a smog check tomorrow or Wednesday?" rather than leaving a message and hoping for a callback that you don't miss either (and have go to voice mail).

Being able to have a voice appointment scheduling system (assuming that it isn't being jail broken https://www.youtube.com/shorts/GJVSDjRXVoo ) could be useful... though there are problems with giving it agency over decisions ( https://www.bbc.com/travel/article/20240222-air-canada-chatb... ).