Nothing huge but the network might "cause devastating interference" to GPS devices.

A new set of government tests showed that LightSquared's proposed mobile broadband network disrupted the signal strength to all GPS devices in the test area, dealing another setback to the company's startup plans. While all global-positioning system devices tested were affected, the severity of the loss of service varied, said Deane Bunce, co-chair of the National PNT Engineering Forum, a federal advisory group of engineers that oversaw the government tests. Mr. Bunce, speaking at a federal government advisory group hearing Thursday, said some devices lost signal strength while others were knocked out completely. For example, the government tests found that General Motors Co.'s OnStar system saw a "significant degradation of service" on most receivers tested.

[...]

LightSquared's airwaves are located close to the airwaves used by GPS receivers, which can be overpowered by the wireless start-up's signals. "It will cause interference. It will cause devastating interference," said James Kirkland, vice president and general counsel of Trimble Navigation Ltd., a GPS maker. "There is not a solution here. In our view it's time to stop squandering resources on this and find alternative spectrum for them."...The government tests suggest that LightSquared's GPS issues are more wide-spread than previously known. Last week, construction giant Deere & Co. reported that during recent testing in New Mexico, LightSquared's network hobbled it's GPS systems more than 20 miles away. Local law enforcement also reported police cars and ambulances lost GPS signals.

[WSJ]

Related: Harbinger Capital Will Pay Redemptions…In Illiquid LightSquared Equity