"This action drove up e-book prices virtually overnight, " said Sharis Pozen, head of the DOJ's antitrust division, at a news conference on Wednesday.

CNN: Will Apple lawsuit mean cheaper e-books?

"T-Mobile has been an important source of competition among the national carriers, including through innovation and quality enhancements such as the roll-out of the first nationwide high-speed data network, " said Sharis A. Pozen, Acting Assistant Attorney General in charge of the Department of Justice's Antitrust Division.

ENGADGET: US government files to block proposed AT&T / T-Mobile merger (update: companies respond)