It appears that NYC may have been reading about the (planned, sued and not carried out) cell-phone jamming demo at a prison last week and gotten the idea that if everyone else could be prevented from talking to each other, the police would enjoy a tactical advantage. However, their plans do not stop at cellular telephones, 2G, 3G or Nth generation; they envision jamming Media feeds so damage assessment isn't available to attackers, and other radio communications that might be used by or exploited by terrorists.
In the United States that encompasses an astounding array of technologies. Let us start with 3-transistor toy walkie-talkies, CB radios, Family Radio Service, (and the higher power GMRS usually included and illegally used by FRS-buying public), MURS -- a limited channel low VHF service needing no license -- licensed business VHF and UHF, 900 MHz unlicensed Part 15, which includes cordless telephones, 900 MHz exempt (this is a cool radio, frequency hopping and practically indetectible by all but The Black Helicopters). Then add WiFi and its relatives, and 5.8 GHz NII and UWB gadgets. Ham radio too, which at up to 1500 Watts allowed power might be a harder job, though presumably we are considered loyal. (A long superseded US Army manual once listed an increase in Amateur Radio activity as an indication of upcoming guerrilla action.)
I suspect that technology has advanced beyond any agency's ability to shut down all commmunications. In any case, -- and this is why the prison demo was canceled – it's unlawful in the USA for anyone to make, import, market or sell jammers for communications regulated by the Federal Communications Commission.
During WW2, when information was needed on what German forces in France were up to, USAF P47's were called in to shoot up telephone wires and force the Jerries onto the wireless. That may be further then the NYPD is willing to go.
Or is "Speed Limit enforced By Aircraft!" for real?