The Federal Communications Commission (FCC) has approved a proposed spectrum swap between T-Mobile and investment firm Grain Management.As part of the planned swap, first announced last year, T-Mobile will offload its 800MHz spectrum to Grain for $2.9 billion, while scooping up 600MHz frequencies from the company as part of the exchange.The deal will see Grain acquire 4.85MHz to 14MHz of 800 MHz spectrum from T-Mobile in 3,224 counties, with T-Mobile snapping up 10 megahertz of 600 MHz spectrum from Grain in 212 counties.T-Mobile has been trying to shift the 800MHz spectrum following its agreement to acquire Sprint in 2020 for $26bn.The carrier had agreed to sell the spectrum to EchoStar-owned Dish Network for $3.59bn, which was set to operate as the country's fourth mobile carrier. However, that deal fell through when Dish said it was unable to afford the spectrum.For T-Mobile, the 600MHz frequencies will add to its existing spectrum holdings that it uses for its 5G mobile network, with the FCC noting that this spectrum will bolster the carrier's 5G network.FCC: An opportunity for D2DIn the FCC's order, the regulator said it has imposed "strict conditions" to ensure that Grain does not hoard the 800MHz of spectrum, but instead utilizes the assets in a "rapid and meaningful way to support a range of terrestrial services and direct-to-device (D2D) operations."Grain had initially requested an interim build-out deadline of six years and a final deadline of 12 years, though the FCC has rejected this, instead giving Grain a deadline of three and eight years.This potentially paves the way for further D2D deployments in the US."We recognize both the potential value of this spectrum to terrestrial deployments, such as rural carrier offerings and utilities’ private networks, as well as to D2D deployments, which have been rapidly evolving," noted the FCC. "The conditions we impose below are designed to facilitate real, meaningful deployment without delay, including immediate consideration of D2D opportunities. Finally, we defer consideration of waiver requests related to Supplemental Coverage from Space (SCS) use of the 800 MHz licenses until a D2D partner is identified and the relevant D2D applications are filed."The regulator said this will provide incentives for Grain to form partnerships with D2D operators in the near term, stating that it "will consider D2D applications associated with these 800 MHz licenses even if Grain completes its solicitation and files application after 2026."One such satellite player that uses 800MHz spectrum is AST SpaceMobile, which works with both AT&T and Verizon in the US.Indeed, AST SpaceMobile has wasted no time in giving its views on the spectrum transaction, as the company told the FCC it welcomes the deal.