Then it has an international caller id. Most people get so few international calls that they will quickly figure out that it can't be real. If it had a locale caller id it is obviously spoofed because otherwise the call wouldn't have come in from the foreign telco.

Once someone does this, legitimate telephone companies elsewhere will become interested as well, and may "play nice" so long as local laws allow it.

> If it had a locale caller id it is obviously spoofed because otherwise the call wouldn't have come in from the foreign telco.

That is not correct. You can send legitimate calls with spoofed caller id between different countries. Many providers will let you do that. (as in, you can assign a caller id from country A to a call originating from country B to A)

I'm saying that those become automatically illegitimate and Country A should reject them. The only exception is IF the telco in country B agrees to assume legal responsibility in country A.

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.

You can't just remove this - it's a legitimate use case.

For example if you go to another country with your mobile phone, your call will be international, but the caller id would not match the source.

But there are plenty of ways for my phone company to verify that it was my phone. (they might verify a clone of my sim, but that is a different problem that they already have to handle)

It costs a lot more internationally, so I'm not sure how much of a problem it really is. While many people would hate this, the same rule could be applied with "if you're forwarding international connections, you're responsible". Bad interconnects would probably drop immediately with a moderate amount of chaos, while legit foreign partners are found who can filter traffic on their end.

My service provider offers <$0.01/min. calls to many countries.

I have a hunch that no telco wants to entirely block a foreign telco because they would lose money and because of the ensuing chaos.

Robocall friendly service providers intentionally mix robocalls with legitimate traffic to avoid terms of service enforcement. e.g. Robocalls are laundered by splitting across n carriers so spam (identified by bad ASR/ACD stats) stays below each carrier's threshold. https://news.ycombinator.com/item?id=12339739