You can buy a mobile phone jammer on the Internet from foreign electronic companies. Some mobile phone jammers can be fitted with frequency filters, so you only jam certain frequencies.
Teresa Masterson, a writer at NBC10, first encountered the jammer on her morning commute and tipped off NBC Investigators. She told the blog
It should go without saying that such a device is illegal. A jammer, which blocks radio frequencies, isn’t just limited to blocking personal cell phone use, but all communication tools that use these frequencies. What does this mean? Essentially that the jammer that lessens the din of personal conversations on your M-14 bus also has the potential to cut off communication between the driver and dispatch centers or public agencies, which could result in a public safety snafu—or disaster. Mobile phone signal jammers also block incoming calls, which means that if used for an extended period you prevent anyone in your vicinity from hearing pressing, even emergency, news.