Even just giving origin information would help, if the local end of the interconnect ensured calls show the international dial-code as a minimum then that would help; instead we get (in UK) international calls (India, primarily) with caller ID showing a local number (sometimes your own number, I think) ... the interconnect certainly shouldn't be facilitating that.
SS7 its the primarily utilized protocol stack nowadays. The PTSN (Public Telephone Switching Network) and the Internet have been combined for a while now.
The problematic part of SS7 is it allows for setting arbitrary unauthenticated origination info in the rough equivalent of a "From" field in the initiation process.
There are attempts ongoing to attempt to implement a "Web of Trust" layer a la TLS on in front of the preexisting telephony infrastructure in the form of STIR/SHAKEN, but it'll have some of the same warts that current "Web of Trust" implementations now currently suffer.
It was my understanding that in PSTN at country-level boundaries the operators choose to forward calls, and do billing and such recording: at that point they decide whether to put the call to the local country network or not. If the call has meta-data as if its come from the local country then they could drop the call request, but they establish the voice call [because call senders pay more than call receivers, presumably].
