How about putting a small tariff on every phone call originating from countries that do not shut down these fraudulent call centers? The tariff perhaps could be as small as 2 or 10 cents per call to make these operations unprofitable. I'm sure that the telecom operators in the foreign country could easily track down (or already know precisely where to find) the call centers. Once the fraud falls below a threshold the…
My understand use these call centers use VoIP providers in the country though. The traffic crossing the border is likely just an encrypted stream, indistinguishable from some VPN or other generic service. The VoIP providers are getting paid (by the scammers), your cell/phone company is getting paid twice (by both you and the VoIP provider). It's not like customers are switching to the other spam-less phone option, or…
Saying "oh there's no way to know where the calls come from" is just lame excuses. CallerId spoofing is one thing, but POTS has other systems.