Our voice phone systems are seamlessly federated. You can call people across carriers, over national boundaries, instantaneously, and the only friction is slightly more numbers to dial.
SMS is also remarkably well federated. In the early 2000s, every carrier had their own text messaging platform. Today, you can send an SMS to practically anyone.
@evan oh, ho, but just you try and join that club now...
You'll need spectrum, and an operating license from a member state of the ITU - which only accepts membership from full UN members.
Good luck...
@steely_glint oh, yeah, I'm not saying it's great. It takes a lot more to break into telecom than to start a Fediverse server.