More worryingly, an aviation device Garmin sells lost its GPS fix at a distance of just under 14 miles away, and was totally jammed five and a half miles away ().

And that's caused by a single transmitter. Cell phone towers work by being part of a grid of many transmitters that hand calls to and from each other. With multiple transmitters in a town, GPS would in all likelihood be killed dead, and within range in the skies above too.

However, LightSquared is confident that it can , saying that its "rollout of full commercial service will satisfy the concerns about the possibility of inadvertent harmful interference to certain GPS devices."

In other words, it's LightSquared's word against Garmin's.

Elsewhere in the world, the European Union is proposing that old analog TV frequencies around 800MHz be used for European 4G networks now that everybody has moved to digital TV, which uses a different and smaller frequency range. However, cable TV services in Europe still pipe data down coaxial lines at these old, analog frequencies. Using a European LTE phone in a room near a cable TV box has been proven to disrupt the image and disrupt data services. ( for a study undertaken by a U.K. government agency proving the effect.)