Federal law prohibits the marketing and operation of cell phone jammers

[Wrightwood]

On February 9, 2011 the FCC cited DealExtreme, Hong Kong for marketing in the United States unauthorized radio frequency devices for jamming cell phones.

Here's the citation:
http://www.fcc.gov/eb/Orders/2011/DA-11-248A1.html

I find it interesting that DealExtreme's website still seems to be marketing the devices without any mention about being illegal in the US.

http://s.dealextreme.com/search/cell+jammer

[in my dreams]

Interesting. I've never met anyone who had one, though, who thought they were legal (coughcough high school teachers...)

[MMB]

Does anyone know if local small time radio stations use those to block specific radio wave transmissions of competing stations?  Sometimes I'm listening to music or news on one station and when I get close to a specific area, that station gets briefly taken over by another station, and I'm wondering how that annoyance is caused?

[SNOW]

If you are listening to an FM station with a somewhat weak signal at your location, a station on an adjacent  frequency with a much stronger signal will sometimes cause your radio to lock onto that one. This is a normal characteristic of FM receivers.

[SkierBob]

I own two.  The better one blocks 3g 4g.  I've loaned it to my friend who is a high school english teacher and uses it in his classroom.