Oh, you can be assured that the profit margins for roaming are 99%+, and if they aren't, it's because of unrelated wastage.

Because ever since the internet was invented, it has obviously become very, very, very cheap to send data all over the world. And this is what we're talking about: your SMS needs to go from the provider in country A to provider in country B. How does it do that? Via a standardized protocol over the internet. How much does that cost? Nothing, all the network components have an internet uplink anyway.

The only thing left to explain high roaming prices is market failure, hence the need to intervene by the EU. Only we had the market failure pour its money into the EU, so it's very far off from the regulatory intervention that should have been made.