T-Mobile’s Sprint Takeover Boosted Mobile Phone Bills, Suit Says

T-Mobile US Inc.’s 2020 acquisition of Sprint Corp.reduced competition and led to higher prices for all US mobile phone customers, an antitrust lawsuit alleges.

The suit was filed Friday in Chicago federal court against against T-Mobile parent Deutsche Telekom AG and former Sprint owner Softbank Group Corp. by Illinois and Indiana customers of AT&T Corp. and Verizon Corp. The plaintiffs are seeking class action status.

Before the deal, when Sprint and T-Mobile were aggressively marketing their services, the average price of nationwide wireless plans dropped 6.3% a year, but since then, “the three surviving carriers have no reason ...