The POTS (plain old telephone system) is explicitly designed for discoverability. They used to physically throw a book that mapped numbers to names and addresse

The POTS (plain old telephone system) is explicitly designed for discoverability. They used to physically throw a book that mapped numbers to names and addresses on your doorstep for free, and chained the same directory to every public telephone. Fighting against a fundamental design goal of a system is a fool’s errand. The features you are looking for can be easily accomplished over the internet, and they smell very similar to PGP and also feel pretty adjacent to Signal/WhatsApp with some variation. Heck if we’re limiting it to off the shelf consumer solutions, FaceTime with custom email domains matches the description if you squint hard enough. The vast majority of people find what you are describing to be completely impractical to the point of uselessness.