https://phys.org/news/2018-06-verizon-sales-brokers.html

Verizon, the nation's largest mobile carrier measured by subscribers, said that about 75 companies have obtained its customer data from two little-known California-based brokers that it supplies directly—LocationSmart and Zumigo.

The company made its disclosure in a letter to Sen. Ron Wyden, an Oregon Democrat who has been probing the phone location-tracking market. Last month, Wyden revealed abuses in the lucrative but loosely regulated field involving Securus Technologies and its affiliate 3C Interactive. Verizon says their contract was approved only for the location tracking of outside mobile phones called by prison inmates.