http://en.wikipedia.org/wiki/Mobile_phon…

Answer:
A phone jammer transmits low power radio signals to cut off communications between cell phones and cell base stations. It does not interfere with any communications other than cellular phones within the defined regulated zone. Upon activating a phone jammer, all idle phones will indicate “NO NETWORK.” Incoming calls are blocked as if the cellular hand phone were off.

When the phone jammer is turned off, all cell hand phones will automatically re-establish communications and provide full service.

get them from one of these sites

http://www.phonejammer.com/

http://www.globalgadgetuk.com/Personal.h…

http://www.globalgadgetuk.com/cell-phone…

Answer:
Legalities

Since these jammers actively broadcast radio signals they might or may not be legal to possess or operate based on the specific laws of the area one is in.

* Armenia : legal[

* Australia: Illegal.

* Belgium: Illegal to sell, possess and operate (licensed part of the spectrum).

* Canada: Illegal.

* Czech Republic: Illegal.

* Finland: Illegal.

* France: Still legally used inside jails.

* Germany: Illegal, but installation in jails has been proposed.

* India: Government and schools use jammers.

* Italy: Technically not illegal to own, but illegal to operate, since the Italian law specifically prohibits to interrupt radio and telephone communications. GSM jammers are however legal to be used in places like hospitals, churches, motion picture theatres and other places with performances, and other buildings where and when the use of mobile telephones may result in a leak of sensitive information: on such occasions, jammers are legal as long as their operation doesn't interfere with electronic medical equipment (such as pace-makers) and grants mobile phones to make emergency calls. Tri-Band Jammers are reserved to, and in use with, the police forces and are being experimented in prisons.

* Mexico: Legal inside jails, often used also in churches and hospitals.

* Turkey: Illegal. Only the police and the military use jammers.

* New Zealand: Legal inside jails.

* Norway: Illegal to own and operate. The police and the military can use jammers in situations in which it is necessary.

* Pakistan: Legal inside banks, often used also in libraries.

* United Kingdom: Illegal to use, but legal to own.

* United States: Illegal to operate, manufacture, import, or offer for sale, including advertising (Communications Act of 1934), with fines of up to $11,000 and imprisonment of up to one year.