Telemarketers have ruined the phone network for me. I haven't answered an unknown call for the past 10 years, which sometimes means I miss important ones. 99.9% of all calls are an attempt to get money, and the 0.1% that's a dentist appointment, a friend that changed numbers or whatever become collateral damage.
A ban is the right idea but I wonder how they can handle it, logistically. I think there needs to be a technical solution.
A national "whitelist", where hospitals, doctors, utility companies and such can register to get their numbers whitelisted perhaps, combined with a setting on phones that block any non-whitelist number.
Each country could maintain their own whitelists, and corrupt nations selling whitelist status to scammers would get blocked in any other country at least.