Currently jammers & cellphones are banned in-flight operations.  Soon they
would be buzzing with ringtones.  Recently the communications authority
has proposed to allow passengers use mobiles on planes.

Jammers were originally implemented by law enforcement agencies. The prime reason: They wanted to crack down any suspicious communication. The targets were the terrorist. The modern technology enabled terrorist attacks have seen higher usage of cell phones as a device to trigger bomb explosions.

According to  FCC aCT, 1934  ”IT prohibits any person from willfully or maliciously interfering with the radio communications of any station licensed or authorized under the Act or operated by the US government.”  First time offenders may face either fines of up to $11,000 or a year in prison for each violation.

Currently jammers are banned in US and are only used by federal law enforcement officials.   State prisons, California and jammers manufacturers are urging it be used in prisons. This might take out the technology in mainstream.

Cell phone jammer blocks transmission/reception of signal by creating interference at the same frequency ranges that cell phones use.   After which a cell phone  will lose the signal or signal quality will deteriorate.
Sale of cell phone jammers is legally prohibited in US.

For as little as $400 you can annoy thousands of people around you. This particular device can jam WiFi and bluetooth signals. The gadget is expected to be released very soon.