Back in the day when I had my first cell phone things were not that far from this. Except that usually it was free/cheap to call people that were on the same carrier and price to call other carriers was ludicrous.

The problem is that social networking protocols would inherently be much more complex than phone protocols (but it could be done). Moreover, some body would have to standardize those protocols as well as discovering some way of preventing spam. My hunch that I know get more spam on my phone number than either my email or my Facebook account because phones still have open points of entry.

I suspect there are two reasons we get more spam phone calls:

1. There's no effective signing on phone calls, so spoofing a phone number is easy. This makes it impossible to prosecute spammers.

2. There's no way to filter a phone call based on the content of the phone call before it arrives. It's possible to spoof senders on email and text messages as well, but it's also possible to filter these based on content before they reach your inbox. This isn't perfect, but it greatly reduces spam in text-based mediums.

The main reason is the telcos choose not to, because they make money on them.

You can eliminate ~95%+ of junk calls from the telco side.

How?

The open protocol could start small and gradually grow over time, maintaining backwards compatibility.

The incentives aren't there, of course.

For starters, let's just have them open, and let the market figure out how to bridge them. With lessons learned from that, maybe we can come up with something working.

But even if not, it would already be a drastic improvement on what we have.

Facebook lets you share posts from Twitter and Instagram, not sure about what else

When you share a post on Twitter or Instagram, you're creating a Facebook share--this isn't an example of an open protocol in any way.

Umm, Facebook owns Instagram.

Except it takes 30 seconds and it’s free to open a facebook account. You can even use messenger without having a facebook profile.