But aren't calls and data encrypted when transmitted through the normal network?But these things have been around for years and years. The don't have to be the size of a suitcase, either. One of the ways that people create no-cell zones, say in a theater, is they bring in a small unit in their pocket that mimics a cell tower. It doesn't have to be high power since it is much closer to the cell phones in the theater than the nearest real cell tower is (probably). It thereby tricks the cell phones into connecting to it instead of the real tower and then simply doesn't complete the calls or route calls to it. But they can also be used to sniff whatever information a legitimate tower could access or to act as a man-in-the-middle attack on conversations.