I don't know if this gets much personal use, seems real cumbersome.

But this is of huge interest to carriers, since it allows them to skip the PSTN/peering cost when the callee endpoint is an IP phone.

There is private ENUM for carrier use I recall, not sure what the current status is, with LTE/VoLTE, RCS etc.pp.

http://dam3d3.free.fr/PFE/Pathfinder/GSMA_PathFinder_WebSite...

Here the list of countries that have ENUM delegated for their country code.

https://www.itu.int/en/ITU-T/inr/enum/Pages/delegations.aspx

Time travel.