That's not true. Phone companies have to pay fees when they have to pass a phone call through their telco to another. They have entire routing table fees involved and the telcos will pass traffic through the cheapest routes. That's why a call route can go through one set of routing in the morning but by the evening it can go a completely different way, it's cheaper the second time around. The fees are constantly changing. From a receiving telco side, they receive an incoming call that's identified themselves as Telco1, which matches the routing tables. The problem is the telcos rely on an honor system when they self identify.(I don't know when this started, it was in place when I worked in telco and everyone I knew at retirement age said it had always been that way for them.) And then we have telcos that go even further and completely avoid identification altogether. Which is sleazy but happens very often. The incoming telcos then are faced with either denying the incoming calls altogether (but then it's the callers that suffer -but it would force the telco trying to pass traffic for free, to either identify themselves or find another route) or risking passing that traffic and not being paid for it. If it's low enough traffic, it's probably easier just to let the calls through without knowing who to charge, so that telco got their calls passed for free. It was a constant game for us to deny traffic and keeping up with the routing tables.

tldr: The technology isn't the only thing that's over 100 years old, the business practices are also extremely broken too. And telcos are not an honest bunch.