Via @azolnai I learned about the 2012 Defense Authorization act that may prevent LightSquared, or anyone else, to interfere in any way with military GPS. Related, last week, Slashdot discussed a story named LightSquared Says GPS Tests Were Rigged.
From the NewScientist article: "A clause buried deep in the 565 pages of the 2012 Defense Authorization act passed in December bars the Federal Communications Commission from approving systems that interfere in any way with military GPS. The bill also tells the FCC to supply Congress with a final copy of the report from its working group, which late last year issued a preliminary report warning that a system proposed by telecoms firm LightSquared of Reston, Virginia would cause serious interference. [...] The concern was that signals near the 4G transmitters would be so strong that that would drown out the faint satnav signals reaching the ground. A series of subsequent tests backed up those claims."
The Slashdot story summary: "Would-be cellular carrier LightSquared claims that the company's LTE network was set up to fail in GPS interference tests. 'Makers of GPS (Global Positioning System) equipment put old and incomplete GPS receivers in the test so the results would show interference, under the cover of non-disclosure agreements that prevented the public and third parties from analyzing the process,' LightSquared executives said on a conference call with reporters Wednesday morning."