[viraptor]

If appropriate laws existed, you could still put pressure on them. Something like "if your international partner sends more than X spam calls, you're responsible for them". The telco would have a choice of getting fined or dropping the interconnect / filtering that source. On the other side, the telco in Bangalore doesn't want to lose the ability to handle calls to the US, so starts monitoring itself.

[MichaelApproved]

International phone companies could be required to put up a bond that citizens could sue against.