Behind the anti-spam measures are a set of protocols, known as STIR and SHAKEN, that ensure incoming callers are who they say they are.

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“These standards combat illegal caller ID spoofing, which occurs when scammers temporarily hijack a phone number to match the area code and 3-digit prefix of the person they are targeting, making the incoming call look familiar,” T-Mobile said in a release.

The system, which is not unique to T-Mobile, works similarly to much of the Internet and its handling of secure traffic.

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Take a hypothetical call involving customers on two different wireless carriers. Under the protocols, when one customer places a call, his or her wireless carrier analyzes the source to be sure it’s really associated with the correct number. Then, before the company hands the call over to the receiving carrier, it attaches some encoded information known as a signature. The receiving carrier analyzes the signature against a trusted third-party database — which all the carriers will have agreed to use — to determine that the signature is valid. Then the call will finally be passed to the intended recipient.

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T-Mobile’s limited rollout — working only on calls within its own network and then only on specific devices — reflects that the program is in its early stages.

But the rest of the wireless industry has eagerly gotten on board, painfully aware that spoofed calls are a drag on the customer experience. Last year, Verizon pledged to launch its own implementation of STIR (Secure Telephone Identity Revisited) and SHAKEN (which stands for “Secure Handling of Asserted information using toKENs”), with a mainstream rollout sometime this year.

Verizon said it successfully deployed the technology in parts of its network last year, and plans to begin authenticating calls between customers this year. Sprint did not immediately respond to requests for an update on their progress with the protocols. AT&T said Thursday that it has committed to rolling out caller authentication this year using STIR and SHAKEN, and that it has completed some lab testing in partnership with Comcast.

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The STIR and SHAKEN spam protections add to a slew of programs the carriers have developed to combat fraudulent calls. Many of them compare incoming calls to known lists of spam numbers, for example, or preemptively block calls that have a match on those lists. A recent study by the market research firm HarrisX found that AT&T and Verizon’s networks were effective at blocking more than half of spam calls, while T-Mobile caught roughly a third and Sprint less than 1 percent.