“The majority of users are on limited/tiered plans because it's much cheaper than unlimited,” Susie Kim Riley, the CEO and founder of Aquto, told Ars. Aquto is a key player in zero-rating because it makes technology that automates the process of bringing in new data sponsors, i.e. companies that want to pay carriers for data cap exemptions. Aquto, an AT&T partner since the carrier launched its “Sponsored Data” program in January 2014, also helps data sponsors run their campaigns.