In Germany it is possible to register an ENUM domain for a phone number. This provides a DNS mapping from the E164 number to DNS records, e.g. for IP phones, etc.

Decentralized and under user control, no shitty silos like FaceTime, WhatsApp.

ENUM stands for “Telephone Number Mapping.” It is essentially a bridge between the world of telecommunications and the Internet. With a single ENUM domain, you can combine all your contact options under your familiar phone number:

https://www.denic.de/en/products/enum-domains/