The stakes are high not only for the GPS industry and its users, but also for those who would use LightSquared's network. In approving it, the Federal Communications Commission seeks to boost wireless competition and bring faster and cheaper Internet connections to all Americans — even in remote corners of the country.

LightSquared and the FCC both insist the new network can co-exist with GPS systems. But device makers fear GPS signals will suffer the way a radio station can get drowned out by a stronger broadcast in a nearby channel.

The problem, they say, is that sensitive satellite receivers — designed to pick up relatively weak signals coming from space — could be overwhelmed when LightSquared starts sending high-power signals from as many as 40,000 transmitters on the ground using the airwaves next door.

"The potential impact of GPS interference is so vast, it's hard to get your head around," said Jim Kirkland, vice president and general counsel of Trimble Navigation Ltd., which makes GPS systems. "Think 40,000 GPS dead spots covering millions of square miles in cities and towns throughout the U.S."

[As if we didn't have enough to worry about.]