But the tide is turning.
Japan allows public places such as theaters and concert halls to install jammers, provided they obtain a government-issued license. And last week, France's industry minister approved a decision to let cinemas, concert halls and theaters install them - as long as provisions are in place so emergency calls can still be made.
Canada had considered allowing blocking in similar situations. But Industry Canada, which regulates the country's telecommunications, decided against it, saying the devices could infringe on personal freedom and affect public safety by crippling communication with law enforcement and security agencies.
Officials at Netline, which sold its first jammer in 1998, say they are selling thousands of jammers a year and have expanded their business throughout the world.
They're far from the only manufacturers. The devices are sold the world over, with dozens of suppliers selling them on the Internet.
Tokyo-based Medic Inc. sold thousands of its Wave Wall jammers before the government stepped in and regulated their use to venues with live performances. Commuters still buy mobile jammers to shut up chatty train passengers, even though their use is illegal.
In Scotland, businessman Ronnie McGuire, owner of Electron Electrical Engineering Services, imported Taiwan-made cell phone blockers and sold them to hotels, restaurants and bars until a local newspaper reported his activities, which were illegal in Britain.
McGuire has said he will still import the Taiwanese devices but sell them for export only to countries where they are allowed.
Loreen Haim, the director of marketing and sales for Netline, wouldn't say how many devices the company sells per year or what country buys the most.
In Mexico, the main clients have been banks looking to stop would-be robbers from communicating with their accomplices and the Mexican government, which is planning to use them at prisons, Haim said.