AT&T Inc's $39 billion bid to buy Deutsche Telekom AG's T-Mobile USA would let it build high-speed wireless services for more than 97 percent of the United States, it said in a U.S. government filing on Thursday.

AT&T, the No. 2 U.S. mobile carrier, also said the merger would spur innovation and economic growth by letting it improve the quality of its services and build high-speed wireless services for 97.3 percent of Americans.

The company upped its commitment slightly since it announced the deal last month.

It had promised to reach 95 percent of Americans with a high-speed service it is planning to launch this year.

No. 3 mobile operator Sprint Nextel opposes the deal on the grounds that it would stifle innovation and competition. The deal would make AT&T the biggest U.S. mobile provider.

Sprint argues that about three quarters of U.S. mobile customers would be served by the top two operators if the deal is approved.

Verizon Wireless, the market leader, would become the second biggest mobile provider after the deal. Verizon Wireless is a venture of Verizon Communications and Vodafone Group Plc .

(Reporting by Jasmin Melvin, additional reporting by Sinead

Carew in New York, editing by Gerald E. McCormick and Robert MacMillan)