Here is a nice overview. Maybe slightly outdated by the latest developments, but the concept of wholesale and retail rates is clear https://en.wikipedia.org/wik

Here is a nice overview. Maybe slightly outdated by the latest developments, but the concept of wholesale and retail rates is clear https://en.wikipedia.org/wiki/European_Union_roaming_regulations https://en.wikipedia.org/wiki/European_Union_roaming_regulat...