You're probably correct in that (edit: re-reading this... no, I'm not an AI - some people write this way and I tend to prefer to defuse potential arguments where two people are arguing for the same thing in a thread). Though I would think of the voice LLM system more as a smart answering machine rather than a complete replacement of calling the shop. The normal (preferred) course would be for one of the human staff there to pick up the phone... say before the 5th ring. On the 7th ring, it goes to voicemail... or to the voice LLM augmented voicemail.

If the LLM augmented voicemail is not much more than the business voicemail service that such places have now, is it enough value add?

That also implies other things - such as the capability to integrate with the calendar and appointment system which I'm still in the very hesitant side, but it could be an interesting service add on if it was properly limited.