Through an effort dubbed “Scam ID,” the carrier said it will start analyzing incoming calls to its customers and comparing the originating numbers to a database of tens of thousands of known numbers used by scammers. The system will issue a warning to the customer’s phone if a caller’s number matches one in the database. Customers can also choose to simply block all calls identified by the system.

Photo credit: T-Mobile

The current epidemic of scam calls involves everything from fake vacation offers and bogus charities to counterfeit car warranties and tax refunds. Lately, scammers have been asking “can you hear me” so they can record a consumer’s voice and use it to authorize unwanted charges. Phone scammers stole $7.4 billion from some 27 million victims in 2015, according to a survey by Harris Poll.

Consumers can already use third-party apps like Nomorobo to block scam calls, but T-Mobile is building its free service into its network, making it easier for consumers to use. The carrier is also part of an industry group working with the Federal Communications Commission to find better ways to stop unwanted and illegal calls. This week, the FCC proposed rules to make it easier for carriers to block robocalls from non-existent or spoofed phone numbers.

T-Mobile said its Scam ID service would be available for new and existing customers on its postpaid One plans starting April 5. MetroPCS customers get the service later in April, the carrier said. And other customers will get Scam ID “over time,” T-Mobile said.

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The carrier warned that the system is not perfect. “Enabling Scam Blocking may inadvertently block desired calls,” T-Mobile (TMUS) warned in the fine print of the new service. What’s more, the system won’t identify or block all annoying phone calls. Many robocalls and other unwanted sales calls that pester consumers won’t be blocked if they are made by legitimate businesses.