"We're in an arms race with these scammers, and we've got to join forces as an industry to keep all wireless customers protected," T-Mobile CEO John Legere said in a press release.

T-Mobile is also expanding its Caller Verified feature to 23 smartphones. Soon, customers with more devices will see "Caller Verified" on their screens when a non-spoofed call arrives from a T-Mobile or Sprint number.

T-Mobile and Sprint are not the first carriers to use the STIR/SHAKEN standards or to team up to verify cross-network calls. AT&T, Comcast and Verizon (Engadget's parent company) offer the anti-robocall tool, and Comcast and AT&T verify calls between the two networks. The FCC has voted to allow carriers to block robocalls by default, so we may see more carriers adopt spam-blocking tech in the near future.