Back in the dark ages of the internet (90's) there was this thing called EMail where mail servers trusted everyone.
Then unscrupulous people started abusing the system. Any IP address could send email via any trusting server to millions of address's for next to nothing. Servers allowed open relay, didn't check for valid email reply to address's, reverse check domain mx records, etc ...
Then smart people started to implement solutions to stop the spam. Mail server configurations were changed. Open relays disappeared, Website submission forms were fixed. Reply to address's were validated, MX records were checked. Many other tricks were implemented, some active, some passive. Antispam examination of email contents improved.
No one change eliminated the problem. But each change in turn helped reduce the flow.
Today, I get less much less than %1 spam even though I have the same email address that I have been using for almost 20 years.
Now voice communications is facing a similar problem.
With the introduction of voip service providers, it is to easy to initiate a voice call from anywhere in the world to anywhere in the world for next to no cost. The traditional phone carriers, for the most part, are able to do very little. The voip carriers are exempt from many of the restrictions that the traditional carriers face. In the days of analog, it was next to impossible to "hack" into the system. Today anyone with a little knowledge, a computer and an internet connection is able to "hack" into the voice system.
If your using voip for your voice communications, you are not going to get any help from the traditional phone carriers. With the protocols so open, the carriers (traditional and voip) are able to do very little. But, over time, changes will be implemented that will improve the system. Little by little things will improve until, 20 years from now, no one that still uses a phone will remember what it was like "Back in the "20's"".