Problems are international calls are already in a technically deficient state. e.g. caller IDs are not sent properly and a generic dummy is sent. Telco 1 uses Telco 2 to connect to Telco 3 which finally terminates on Telco 4's network and rings the phone.

There are literally treaties that govern phone traffic that would have to be updated. Most telcos are a monopoly or oligopoly and don't care about customer dissatisfaction. It's not like there's a substitute to the PSTN ready to go. Are you going to tell all of your contacts you are only reachable through Skype/Hangouts/Facetime? Cutting off a spammy foreign telco would also hurt revenue.

Frankly, the definition of telecom fraud should include corporations ripping off their customers not just petty criminals getting free calls.