From GAO:

We also interviewed representatives from the four largest U.S. wireless carriers (Verizon Communications Inc., Sprint Corporation, TMobile US, Inc., and AT&T Inc.); an industry trade organization (5G Americas); small businesses (Celona, Inc., Edge Compute, Inc., Prime Lime Consulting, and Wickr); standards bodies (the Institute of Electrical and Electronics Engineers and the Alliance for Telecommunications Industry Solutions); and policy organizations (Electronic Frontier Foundation and R Street Institute).116

116 Sprint Corporation merged with T-Mobile US, Inc. on April 1, 2020, and the merged company is known as T-Mobile. At the time of our interviews they were separate companies.