* "Caller Verified is T-Mobile’s implementation of the STIR and SHAKEN standards" 
* "Verizon reiterates both our commitment to deploying the STIR/SHAKEN call authentication technology" 
* "Sprint supports efforts to build the SHAKEN/STIR call authentication system" 
* AT&T doesn't seem to mention STIR or SHAKEN by name on their robocall page  but the FCC sent them a letter thanking them for their "commitment to implement a robust call authentication framework in 2019" 
* "Comcast is proud to be at the forefront of efforts to address the scourge of illegal spoofed robocalls in this country, including the development of the end-to-end call authentication protocol known as SHAKEN and STIR"