1) Emails are decentralized and the telephone network is much less so. It's controlled by a relatively small number of companies. I can't run my own server and connect it to the VoIP network and start sending packets. The major companies can all agree to ban caller ID spoofing and block any carriers that allow it to happen, or at least block any of them for domestic numbers. But they don't.
2) We actually have kinda solved the caller ID problem with email. We have SPF and message signing and the Telco industry seems to be dragging their feet to implement equivalent caller ID verification technology. Imagine if you could block a spam caller and report their endpoint on the telephone network. They'd at least have to purchase a new number each time this happens, rather than just impersonating as they do now.
> Emails are decentralized and the telephone network is much less so. It's controlled by a relatively small number of companies
E-mail is largely controlled by a small number of companies. The vast majority of people use Microsoft, Google or Yahoo Mail. The reasons it's not centralized is the same as with phone numbers - interoperability.
As you note, all the major e-mail providers already implement SPF and DKIM which is more advanced than anything the carriers are talking about implementing. Spam remains a problem. I think spammers will evolve the same techniques of attacking and taking over "valid" endpoints and routing traffic through them as they do with e-mail today. Of course, this is a good thing. It raises the expense and risks associated with spam phone calls. Still, I think the claim that any technical measures will stop these calls is unhelpful hyperbole.
Ultimately the only way to actually stop these is to starve these services for funds which will be lobbied against heavily by large players who rely on these services (knowingly or unknowingly) to drive sales.
Is email truly decentralized? Roll your own and you'll encounter issues with deliver ability just from being new in the market. Large providers manage their own block lists and prevent some messages from some ips being delivered at all. This is a practice that shuts down decentralization and creates an oligopoly, although I agree it isn't as severe as the tele situation.
There are ways to enter the VoIP market by purchasing trunk access but iirc that's still controlled by a few big players.
Another difference is that email in your junk folder still contains the information. Blocking a spam call means no information gets stored.
2) We actually have kinda solved the caller ID problem with email. We have SPF and message signing and the Telco industry seems to be dragging their feet to implement equivalent caller ID verification technology. Imagine if you could block a spam caller and report their endpoint on the telephone network. They'd at least have to purchase a new number each time this happens, rather than just impersonating as they do now.