Putting those topics aside for a moment, I'll point out that multiple districts have asked me over the years about simply 'jamming the signal' to prevent unauthorized use of these devices on school grounds. They're referring to the purchase of electronics that would be placed in a school to intentionally interfere with the signal.
Be aware of what the law says about this matter! To put it pretty plainly, everything I've read says that intentionally jamming a cellular signal is illegal. This topic makes for some interesting reading and, as the links below indicate, I don't think anyone has been prosecuted for violating this law. That doesn't change the fact, though, that this is against the law. The text is a quick read, so I'll just include it:
The operation of transmitters designed to jam or block wireless communications is a violation of the Communications Act of 1934, as amended ("Act"). See 47 U.S.C. Sections 301, 302a, 333. The Act 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 U.S. government. 47 U.S.C. Section 333. The manufacture, importation, sale or offer for sale, including advertising, of devices designed to block or jam wireless transmissions is prohibited. 47 U.S.C. Section 302a(b). Parties in violation of these provisions may be subject to the penalties set out in 47 U.S.C. Sections 501-510. Fines for a first offense can range as high as $11,000 for each violation or imprisonment for up to one year, and the device used may also be seized and forfeited to the U.S. government.
I've had at least one person speculate that schools, hospitals, etc are public entities that are given waivers and can legally purchase these devices. I don't agree with that and would say that, if it were legal, why would you see articles like this that detail the struggles that prisons are having with cell signal issues? In addition, gear sales sites go to great lengths to point out that only a small group of federal agencies have the right to legally purchase such technology in the United States.
Interesting topic, but I thought I'd take a few minutes to point out that I haven't found a single thing that would allow a school district to purchase electronics to jam cell phone signals without violating federal law.
Spy gear site w/ interesting test re: legality of 'jammers'