Any method someone brings up may help by around 20%, but that's really it.
The issue for most of these spam callers are two fold:
- For the scammers, they are generally spoofing numbers. Many people who have worked at a company with a direct phone number can tell you they've at least received one call, in the last year or so, from some random person telling them to stop spam calling them. This is because the scammers are spoofing that particular number. But, in reality, that number is NOT a spam number. It is a legit number for a legit company/organization. Also, have many people can attest to calling someone only to be told by that person that their number shows up as "Spam Caller". This is because some scammer is out there spoofing that number and enough people on a particular cellular carrier have reported it as spam. When this happens, you have to fill out paperwork for each of the major carriers to submit and remove your number from the "Spam Caller" list for THAT carrier. BTW, spoofing a phone number you do not own is actually illegal and should be reported to the FCC, though there's not much they can do about it.
- The other situation comes from legit organizations like non-profits, political/campaign calls, etc. These are not really "scammers" per se, but are simply cold callers (though many still consider these spam calls). For some of these, they use a DID that is owned AND MAINTAINED by that particular organization/company. However, for a lot of these types of situations like outbound calling campaigns, they spin these up as needed. When they decide to spin these up, they get a fresh block of DID's from their carrier and display those. These numbers can be reported enough to get added to national directory of spam callers, but they will just have a new number during the next campaign, which is NOT on the registry.
No app you can download can truly stop either of these. I have customers all the time who call and ask for magic. I always tell them to stop and think about what they're asking. How does the app know it's a spam caller? What data is it using?
The only data any app can use is the exact same data every major carrier has access to.
TLDR: Any "solution" you look at may improve your experience by around 20-30% for a little while, but there is not sure-fire way to block spam callers aside from White-listing numbers instead of blocking them. White-listing is the only way to truly block spam callers.