I'd assume regulated in the sense of identity verification and transactions. There's no legal basis for needing a north American phone number, but good luck with any US obligations if you are without one.
I’m wondering how feasible would it be to just use a SIM card from another country (e.g. in Estonia, you can get a prepaid card for 1 € that works in EU roaming just fine, with domestic-like prices on local calls). How many services in Germany require you to use specifically German number?
It depends of course how far you are. I used to use an orange Spain SIM before the EU roaming deal because they had free roaming on sister networks. But I didn't go there so much.
