It's not a new idea, seeing as Google pretty much announced this years ago. I don't know how much uptake it got (it isn't available in my country) but it's definitely one of the main real-world use cases of LLMs and related AI that I can see surviving the bubble. If you can get enough money out of it to pay for your service costs, that seems like an excellent tool.

That said, my experience with LLMs is that they tend to lie/misrepresent user input and intention, especially when translating text. Doesn't sound like a problem to me if you're just ordering pizza or scheduling a haircut, but when it comes to healthcare, that might become problematic. Furthermore, there are quite a few regulations when it comes to healthcare services that you might need to double check, just to make sure you're avoiding having to comply with difficult and expensive regulation. Not really an issue for a tool built for your parents, but when you're marketing it to people (especially vulnerable groups, like people not speaking the language of the country they're in).

Also, does this bot announce that it's a bot?

Also, how will you prevent scam callcenters from ruining your bot's reputation? Is there some kind of abuse detection in place? Because if you just have a service that will call people and tell them what you instruct it to tell them, I can guarantee that malicious people will flock to it.