More specifically, the deal will allow AT&T to have increased presence on the 2.3GHz band (WCS), 2110 - 2155 MHz downlink AWS, as well as 1710 - 1755 MHz uplink AWS. However, the carrier won't be able to utilize its new purchase right away, or at least the WCS part of it. The spectrum hasn't been used for wireless data connections, because it may interfere with the adjacent satellite radio frequencies. However, in June, AT&T and Sirius XM have filed a proposal with the FCC that will supposedly get rid of any possible interference. The solution is still being reviewed by the FCC.
Aside from the new spectrum that AT&T has gotten its hands on, the interesting thing about this acquisition is that AT&T is actually buying the company itself for $25 million plus a contingent payment of about $25 million more. The other $550 million will go towards retiring NextWave Wireless's dept.