One of my kid's schools had a wild debate about this for their yearly charity "Readathon." The kids get sponsors to sign up to pledge the amount of money they will donate for each book the kid reads during the readathon. Parents are expected to sign off that their kid really did the reading for all the books they put on their sheet. Other than that its on the honor system. They've been doing it for 60+ years.
The kids don't get any prizes but they do get certificates of recognition for various levels of achievement. It came up this year, that some parents count audiobooks and others don't. They have been doing it like this for ome years now but it was never discussed before. The rules don't say anything about audiobooks but they were written back when audiobooks weren't common.
We had some seriously intense discussions in the Parents Charter (the name for our PTA) and lots of people have strong feelings about this! In the end the agreement was that transparency is best so the form has been updated with one side for audiobooks and one side for books. For purpose of donation they are counted the same.
So ideally a handset device capable of recieving and making calls to a limited number of devices.
When you say a "limited number of devices" do you mean a closed system when you have provisioned all the devices or do you mean you also need to be able to receive calls from standard phones?
To replace a landline you can just use a service like Vonage Home for about $10/month. If you want to setup your own PBX (phone system) for calling your own managed set of devices, then you need more. In any case, you always need a SIP service if you want to make and receive calls with regular phone numbers.
I use Windows Server because that's what I know. Though I am curious to learn other OSes when I have more time. I don't use docker so that's really not a problem for now.
I agree and for my kids that is the rule.