LightSquared gained the spectrum to do this by agreeing to build a hybrid system. However, LightSquared isn't joining those networks at the hip. It plans to sell access solely at wholesale and let its carrier partners offer service on either or both of the networks. Because this doesn't fit the FCC's original vision of a unified hybrid network, the company requested a waiver from having to sell both systems together. The price of that waiver was a requirement to solve the interference issue.

Cellular networks such as LightSquared's transmit at much higher power than do satellite-based systems -- as much as 1 billion times as high, according to some critics. In tests, the LTE network overwhelmed GPS receivers, such as in-car navigation systems, that were trying to lock on to weaker signals coming from GPS satellites. At a Congressional hearing last week, federal officials and GPS industry representatives said interference with GPS could endanger critical systems and a thriving industry. GPS device sales total $20 billion per year, and about $3 trillion worth of commerce each year relies on the U.S.-built system, said Roy Kienitz, under secretary for policy at the U.S. Department of Transportation.

One initiative that would be endangered by LightSquared is NextGen, a new air traffic control system designed to improve safety that relies on GPS, Kienitz said. The Federal Aviation Administration and airline industry have already invested $8 billion in NextGen, he said.

Given what's at stake, it's not surprising that a debate over technology has turned political. Last week, the House Appropriations Committee approved an amendment to a spending bill that would block any funding for the FCC to help LightSquared's plans move forward until all interference issues had been resolved. This effort to control the FCC through its purse strings is on its way to the full House for consideration along with the spending bill. The FCC already requires a solution to the interference problem before it will let LightSquared go forward.

"It's really just Congress reinforcing, through the appropriations process, what the FCC has already stated is their plan," said Steve Gilleland, a legislative assistant to Rep. Steve Austria, an Ohio Republican who co-sponsored the amendment.