FYI: T-Mobile's app that they charge $4/month for is a reskin of the Hiya app (https://hiya.com/) that's only $1.25/month when paid yearly.

I just installed it. It identifies many of my recent robocalls as spam. Thanks!

It also allows me to block numbers from my sim area code. This is where most spam calls spoof to be coming from. When I recently called T-mobile to ask for them to do this, they said they couldn't help me.

I'm not entirely sure that is correct, because the behaviour of hiya and t-mobile's offering is different. Hiya will hang up on a spam call, but t-mobile's app seems to make it so they don't even connect to me.

I was using t-mobiles free tier scam call blocker, which worked pretty well except it also blocked calls from Twilio, including our downtime alerts. So I unfortunately had to disable it.

How does it identify spoofed numbers?

The company I work for has a similar feature. We have a tap on the actual phone network (for some carriers) and can track in real time. If we notice that (407)-555-1212 has placed 100 outbound calls in the past 10 seconds, that's probably a robo call. If it's from a phone number that isn't provisioned (or not in use---there are databases for such information) then it's spoofed. Or it could be a valid phone number whose home switch [1] is in Kentucky making dozens of outbound calls per second from the Barbados, it's probably spoofed as well.

[1] At least in North America, each phone number is assigned a "home switch," which will always be notified where (as in "which phone switch it servicing it" not "at 40°58′35″N 80°8′9″W") it is so calls can be forwarded to the proper switch (think roaming).

Thanks. It seems technically possible to stop a great deal of these robocalls with that info.