The phone part is no different. It's easy to run your own FreeSWITCH or Asterisk server at home and connect a cellphone using Wireguard. It costs ~0.5$ US per month to get nearly unlimited everything. Calls and SMS work just fine. The problem is always mobility. You need either Wifi or some of those odd reseller brand ultra cheap pre-paid plans (like "1$ for the first 200mb" plans). Then you need to make sure only the voice/sms is allowed to use the data and you get a 2$ nationwide working cellphone. You can also share someone else plan by having them leaving their Phone wifi hotspot on.
As for reliability, well, that's your problem now, good luck!
> point some metal out of their window and the neighborhood would be happy?
As for reliability, well, that's your problem now, good luck!
> point some metal out of their window and the neighborhood would be happy?
You might, but the FCC won't