Countries plan to deploy jammers in various locations

Japan allows public places such as theaters and concert halls to install cell phone jammer, provided they obtain a license from the government. And last week, France's industry minister approved the decision to let cinemas, concert halls and theaters set them up - as long as arrangements are in place for emergency calls to still be made.

Canada had considered allowing blocking in similar situations. But Industry Canada, which regulates the country's telecommunications, decided not to do so, saying the devices could infringe personal liberty and undermine public safety by crippling communications with law enforcement agencies and of security.

Officials at Netline, which sold its first jammer in 1998, say they sell thousands of jammers a year and have grown their business around the world.

They are far from the only manufacturers. The devices are sold all over the world, with dozens of vendors selling them over the internet.

In Scotland, businessman Ronnie McGuire, owner of Electron Electrical Engineering Services, imported Taiwanese cell phone blockers and sold them to hotels, restaurants and bars until a local newspaper reported his activities illegal in Britain.

Mr McGuire said he would still import Taiwanese devices, but only sell them for export to countries where they are allowed.

Loreen Haim, director of marketing and sales for Netline, won't say how many devices the company sells each year or which country buys the most.

In Mexico, the main clients are banks that seek to prevent would-be thieves from communicating with their accomplices and the Mexican government, which plans to use them in prisons, Haim said.