https://www.theverge.com/2019/1/10/18177008/tmobile-call-verification-spam-shaken-stir-note-9

T-Mobile is beginning to roll out support for call verification technology, which will confirm that a phone call is actually coming from the number listed on caller ID. Now, if one T-Mobile subscriber calls another T-Mobile subscriber, the person receiving the call will see a message saying “Caller Verified” if they have a supported phone. Unfortunately, there’s only one supported phone for the time being.

Call verification won’t put a stop to spammy phone calls, but it will start to help people identify which calls are actually coming from real people. As anyone with a phone knows, spammers have relentlessly spoofed local phone numbers in recent years, making it appear that you’re getting an incoming call from someone you may know. Call verification is meant to combat that.