Dish Network had pushed its own competing proposals for both Sprint and Clearwire, but recently abandoned its bid.
Dish had warned that allowing SoftBank, a foreign company, to own such large U.S. telecommunications networks would pose a threat to national security. Sens. Charles Schumer (D-N.Y.) and John McCain (R-Ariz.) also expressed concern about the SoftBank deal.
After SoftBank agreed to a series of concessions, an interagency panel cleared the deal of national security concerns last month.
Sprint shareholders voted to approve the deal earlier this week.