The telephone infrastructure will be either cellular or terrestrial. With regards to cellular, if the community has 3G as the only connection, then there will be a fast track to upgrade the network to 5G There is no need to move to 4G data if the towers will have to be upgraded anyways. Exception will be VOLTE. It will just make sense to invest in current technology rather than go up one step to yesterday’s technology. For terrestrial connection, all telephone service will use SIP to make and receive calls. This will require a stable and “good enough” connection until better solutions can be rolled out. With that in mind, all telephone will work in sync with internet.
Since there must be at least a minor internet connection for the SIP phone to work, there will need to be a way for such connections. When fiber is not yet available, BPL (Broadband over Power Line) will connect any terrestrial telephone service to the Internet connection that would be need to make and receive calls. Anyone just using phone service only will likely receive a 512kbps connection, and will need a modem for BPL, or a router for fiber. The connection will be enough to handle calls for one line. Additional lines should have a dedicated internet connection.
For cellular phones, 4G and 5G will be the standard. New phones will be smartphones which is like having a computer in your pocket. Since all smartphones are still a phone, they will receive dedicated phone service without the need for a data service connection to the premise.
In new construction, or major renovation, all coaxial lines, and telephone lines will be replaced with RJ45 connections. For telephone, the consumer will use an ATA as above, or buy a SIP phone. This is because there will be no more telephone jacks in the premise, and there will be no more new telephone connections made available. RJ45 is much more versatile, and flexible as one might guess. No matter what, every premise will have a static IPv6 address (except cellular service). This may not sound important for a telephone service, but the IPv6 address will have a database lookup for directing emergency services to the correct address without the caller knowing the address they are at.