US cell carriers team up to combat robocalls — but no deadline set

AT&T, Sprint, T-Mobile and Verizon — have promised to make efforts to prevent spoofed and automated robocalls. Announced Thursday, the pledge comes after 51 U.S. attorneys general brokered a deal that would see the telecom giants roll out anti-robocalling technologies, including a way of cryptographically signing callers to wipe out phone number spoofing. Known as STIR/SHAKEN, the system relies on every customer phone number having a unique digital signature which, when checked against the cell networks, validates that a caller is real.