Polish Secret Service jammed cell phone signals from nurses protesting outside the prime minister’s office. Nurses were inundating the prime minister with calls to his office and disrupted his afternoon nap, so the solution was obvious - shut them up by disrupting their cell phone connections.
Today the scandal is out in full force - the opposition wants answers and the answer is... there is no such thing as targeted cell phone signal jamming.
Signal jamming is a well established and important part of warfare and policing, and now everyone can participate in this game: portable, pocket-sized signal jammers can be purchased online.
Be aware that cell phone jamming may be illegal in your jurisdictions, except when used against you by the military and cops, naturally...
How cell phone jammers work from How Stuff Works.
As with other Radio jamming, cell phone jammers block cell phone use by sending out radio waves along the same frequencies that cellular phones use. This causes enough interference with the communication between cell phones and towers to render the phones unusable. On most retail phones, the network would simply appear out of range. Most cell phones use different bands to send and receive communications from towers (Called Full Duplexing). Jammers can work by either disrupting phone to tower frequencies or tower to phone frequencies. Smaller handheld models block all bands from 800MHz to 1900MHz within a 30 foot range. Small devices tend to use the former method, while larger more expensive models may interfere directly with the tower. The radius of cell phone jammers can range from a dozen feet for pocket models to kilometers for more dedicated units. The TRJ-89 jammer can block cellular communications for a 5-mile (8 km) radius.