Sprint did not immediately return a request to comment.
AT&T, the second-largest mobile carrier, after Verizon, is currently looking to gain government approval of its own smaller spectrum deals with companies including NextWave, Comcast and Horizon. AT&T's statement could be seen as putting pressure on the Federal Communications Commission to approve its deals if the commission also allows Softbank to take over Sprint and Clearwire.
Sprint and AT&T have a history of animosity towards one another. Sprint was a vocal opponent of AT&T's bid to buy T-Mobile last year, and sued to block the deal. The FCC and the Justice Department agreed with Sprint and filed their own actions against the merger.
Regulatory opposition forced AT&T to abandon the $39 billion deal.