Same here, I am amazed by the resiliency and longevity of the service. I'm still not buying the "paid by the radio stations" explanation, but at the same time, I have no idea where the revenue comes from.

One thing I learned from experience is that telecom operators don't seem to like it very much when you call these numbers from a flat rate subscription. I used to call from my daily driver phone, and after a few days it my service got savagely killed without explanation. I had to physically go to one of their stores, the support team had no idea what I had done wrong. I even incriminated myself by admitting I had been calling "strange" numbers, but they said it had nothing to do with that. They said my subscription was active, payments up to date and in good standing in their system. They tried to swap the SIM card, it didn't work. Then they spent almost an hour escalating the issue with their backoffice, finally they managed to restore the service. I asked for an explanation, but none was given. It was a half scary, half funny experience.

After that I contacted OP to relate my experience, he confirmed that it wasn't wise to call from your daily driver line or subscription. I think he should add it to the FAQ, but that would sound kind of shady. On the other had, obvious is obvious

Bottom line is do not attempt to call from a non-burner SIM or VoIP/landline connection but otherwise it's all good, not a scam, at least not for the callers.